I undertook some research into this. My findings are below, but tl;dr: it appears that this now works as expected and the bug can be closed.

---


# Problem

There were reports that resizing an instance from a pinned flavor to a unpinned
one not result in the pinning being removed. The opposite is also reportedly
true.

# Steps

## Create the required flavors

    $ openstack flavor create test.unpinned --id 100 --ram 2048 --disk 0 --vcpus 2
    $ openstack flavor create test.pinned --id 101 --ram 2048 --disk 0 --vcpus 2
    $ openstack flavor set test.pinned --property "hw:cpu_policy=dedicated"

# Ensure this is available

    $ openstack flavor list
    +-----+---------------+-------+------+-----------+-------+-----------+
    | ID  | Name          |   RAM | Disk | Ephemeral | VCPUs | Is Public |
    +-----+---------------+-------+------+-----------+-------+-----------+
    | 1   | m1.tiny       |   512 |    1 |         0 |     1 | True      |
    | 101 | test.unpinned |  2048 |    0 |         0 |     2 | True      |
    | 101 | test.pinned   |  2048 |    0 |         0 |     2 | True      |
    | 2   | m1.small      |  2048 |   20 |         0 |     1 | True      |
    | 3   | m1.medium     |  4096 |   40 |         0 |     2 | True      |
    | 4   | m1.large      |  8192 |   80 |         0 |     4 | True      |
    | 42  | m1.nano       |    64 |    0 |         0 |     1 | True      |
    | 5   | m1.xlarge     | 16384 |  160 |         0 |     8 | True      |
    | 84  | m1.micro      |   128 |    0 |         0 |     1 | True      |
    +-----+---------------+-------+------+-----------+-------+-----------+

    $ openstack image list
    +--------------------------------------+---------------------------------+--------+
    | ID                                   | Name                            | Status |
    +--------------------------------------+---------------------------------+--------+
    | c44bba29-653e-4ddf-963d-442af4c33a13 | cirros-0.3.4-x86_64-uec         | active |
    | 8b0284ee-ae6c-4e80-b5ee-26895d574717 | cirros-0.3.4-x86_64-uec-ramdisk | active |
    | 855c2971-aedc-4d5f-a366-73bb14707965 | cirros-0.3.4-x86_64-uec-kernel  | active |
    +--------------------------------------+---------------------------------+--------+

# Boot an instance

    $ openstack server create --flavor=test.pinned \
        --image=cirros-0.3.4-x86_64-uec --wait test1

# Validate that the instance is pinned

    $ openstack server list
    +--------------------------------------+-------+--------+--------------------------------------------------------+
    | ID                                   | Name  | Status | Networks                                               |
    +--------------------------------------+-------+--------+--------------------------------------------------------+
    | 857597cb-266b-4032-8030-e3cc76ebf0e7 | test1 | ACTIVE | private=10.0.0.3, fd2a:ec16:99e1:0:f816:3eff:fe99:df9f |
    +--------------------------------------+-------+--------+--------------------------------------------------------+

    $ sudo virsh list
     Id    Name                           State
    ----------------------------------------------------
     1     instance-00000001              running

    $ sudo virsh dumpxml instance-00000001
    <domain type='kvm' id='1'>
      <name>instance-00000001</name>
      ...
      <vcpu placement='static'>2</vcpu>
      <cputune>
        <shares>2048</shares>
        <vcpupin vcpu='0' cpuset='1'/>
        <vcpupin vcpu='1' cpuset='21'/>
        <emulatorpin cpuset='1,21'/>
      </cputune>
      <numatune>
        <memory mode='strict' nodeset='0'/>
        <memnode cellid='0' mode='strict' nodeset='0'/>
      </numatune>
      ...
      <cpu>
        <topology sockets='1' cores='1' threads='2'/>
        <numa>
          <cell id='0' cpus='0-1' memory='2097152' unit='KiB'/>
        </numa>
      </cpu>
      ...
    </domain>

# Resize the instance to the unpinned flavor

    $ openstack server resize test1 --flavor test.unpinned --wait
    complete

    $ openstack server list
    +--------------------------------------+-------+---------------+--------------------------------------------------------+
    | ID                                   | Name  | Status        | Networks                                               |
    +--------------------------------------+-------+---------------+--------------------------------------------------------+
    | 857597cb-266b-4032-8030-e3cc76ebf0e7 | test1 | VERIFY_RESIZE | private=10.0.0.3, fd2a:ec16:99e1:0:f816:3eff:fe99:df9f |
    +--------------------------------------+-------+---------------+--------------------------------------------------------+

    $ openstack server resize test1 --confirm

# Validate that the instance is no longer pinned

    $ openstack server list
    +--------------------------------------+-------+--------+--------------------------------------------------------+
    | ID                                   | Name  | Status | Networks                                               |
    +--------------------------------------+-------+--------+--------------------------------------------------------+
    | 857597cb-266b-4032-8030-e3cc76ebf0e7 | test1 | ACTIVE | private=10.0.0.3, fd2a:ec16:99e1:0:f816:3eff:fe99:df9f |
    +--------------------------------------+-------+--------+--------------------------------------------------------+

    $ sudo virsh list
     Id    Name                           State
    ----------------------------------------------------
     2     instance-00000001              running

    $ sudo virsh dumpxml instance-00000001
    <domain type='kvm' id='2'>
      <name>instance-00000002</name>
      ...
      <vcpu placement='static'>2</vcpu>
      <cputune>
        <shares>2048</shares>
      </cputune>
      ...
    </domain>

# Resize the instance back to the pinned flavor

    $ openstack server resize test1 --flavor test.pinned --wait
    complete

    $ openstack server list
    +--------------------------------------+-------+---------------+--------------------------------------------------------+
    | ID                                   | Name  | Status        | Networks                                               |
    +--------------------------------------+-------+---------------+--------------------------------------------------------+
    | 857597cb-266b-4032-8030-e3cc76ebf0e7 | test1 | VERIFY_RESIZE | private=10.0.0.3, fd2a:ec16:99e1:0:f816:3eff:fe99:df9f |
    +--------------------------------------+-------+---------------+--------------------------------------------------------+

    $ openstack server resize test1 --confirm

# Validate that the instance is pinned once more

    $ openstack server list
    +--------------------------------------+-------+--------+--------------------------------------------------------+
    | ID                                   | Name  | Status | Networks                                               |
    +--------------------------------------+-------+--------+--------------------------------------------------------+
    | 857597cb-266b-4032-8030-e3cc76ebf0e7 | test1 | ACTIVE | private=10.0.0.3, fd2a:ec16:99e1:0:f816:3eff:fe99:df9f |
    +--------------------------------------+-------+--------+--------------------------------------------------------+

    $ sudo virsh list
     Id    Name                           State
    ----------------------------------------------------
     3     instance-00000001              running

    $ sudo virsh dumpxml instance-00000001
    <domain type='kvm' id='3'>
      <name>instance-00000001</name>
      ...
      <vcpu placement='static'>2</vcpu>
      <cputune>
        <shares>2048</shares>
        <vcpupin vcpu='0' cpuset='1'/>
        <vcpupin vcpu='1' cpuset='21'/>
        <emulatorpin cpuset='1,21'/>
      </cputune>
      <numatune>
        <memory mode='strict' nodeset='0'/>
        <memnode cellid='0' mode='strict' nodeset='0'/>
      </numatune>
      ...
      <cpu>
        <topology sockets='1' cores='1' threads='2'/>
        <numa>
          <cell id='0' cpus='0-1' memory='2097152' unit='KiB'/>
        </numa>
      </cpu>
      ...
    </domain>