Sure, I did the same test and still got a SIGABRT, but the debug looks a little different:

Backtrace:

#0  0x00007f8f0d46a3f8 in raise () at /lib64/libc.so.6
#1  0x00007f8f0d46bffa in abort () at /lib64/libc.so.6
#2  0x00007f8f0d462c17 in __assert_fail_base () at /lib64/libc.so.6
#3  0x00007f8f0d462cc2 in  () at /lib64/libc.so.6
#4  0x000055ff4ce33926 in mirror_run (s=0x55ff4fc00dd0) at block/mirror.c:335
        next_sector = 31174784
        next_chunk = 243553
        nb_chunks = 29
        end = 209715200
        sectors_per_chunk = 128
        source = 0x55ff4e1eb050
        sector_num = 31171072
        delay_ns = 0
        delay_ns = 0
        cnt = 157184
        should_complete = <optimized out>
        s = 0x55ff4fc00dd0
        data = <optimized out>
        bs = 0x55ff4e1eb050
        sector_num = <optimized out>
        end = <optimized out>
        length = <optimized out>
        last_pause_ns = <optimized out>
        bdi = {cluster_size = 65536, vm_state_offset = 107374182400, is_dirty = false, unallocated_blocks_are_zero = true, can_write_zeroes_with_unmap = true, needs_compressed_writes = false}
        backing_filename = "\000\021"
        ret = <optimized out>
        n = 1048576
        target_cluster_size = <optimized out>
        __PRETTY_FUNCTION__ = "mirror_run"
#5  0x000055ff4ce33926 in mirror_run (opaque=0x55ff4fc00dd0) at block/mirror.c:613
        delay_ns = 0
        cnt = 157184
        should_complete = <optimized out>
        s = 0x55ff4fc00dd0
        data = <optimized out>
        bs = 0x55ff4e1eb050
        sector_num = <optimized out>
        end = <optimized out>
        length = <optimized out>
        last_pause_ns = <optimized out>
        bdi = {cluster_size = 65536, vm_state_offset = 107374182400, is_dirty = false, unallocated_blocks_are_zero = true, can_write_zeroes_with_unmap = true, needs_compressed_writes = false}
        backing_filename = "\000\021"
        ret = <optimized out>
        n = 1048576
        target_cluster_size = <optimized out>
        __PRETTY_FUNCTION__ = "mirror_run"
#6  0x000055ff4ce9968a in coroutine_trampoline (i0=<optimized out>, i1=<optimized out>) at util/coroutine-ucontext.c:78
        self = 0x55ff4f6c2c80
        co = 0x55ff4f6c2c80
#7  0x00007f8f0d47f560 in __start_context () at /lib64/libc.so.6
#8  0x00007ffc759cb060 in  ()
#9  0x0000000000000000 in  ()

I get this in the log:

qemu-system-x86_64: block/mirror.c:335: mirror_iteration: Assertion `hbitmap_next == next_sector' failed.


The system was compiled like this:

Install prefix    /usr
BIOS directory    /usr/share/qemu
binary directory  /usr/bin
library directory /usr/lib64
module directory  /usr/lib64/qemu
libexec directory /usr/libexec
include directory /usr/include
config directory  /etc
local state directory   /var
Manual directory  /usr/share/man
ELF interp prefix /usr/gnemul/qemu-%M
Source path       /tmp/qemu-2.6.0-rc1
C compiler        cc
Host C compiler   cc
C++ compiler      c++
Objective-C compiler clang
ARFLAGS           rv
CFLAGS            -pthread -I/usr/include/glib-2.0 -I/usr/lib64/glib-2.0/include -g -O2 -fPIC
QEMU_CFLAGS       -I/usr/include/pixman-1 -I$(SRC_PATH)/dtc/libfdt -DHAS_LIBSSH2_SFTP_FSYNC -fPIE -DPIE -m64 -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -Wstrict-prototypes -Wredundant-decls -Wall -Wundef -Wwrite-strings -Wmissing-prototypes -fno-strict-aliasing -fno-common  -Wendif-labels -Wmissing-include-dirs -Wempty-body -Wnested-externs -Wformat-security -Wformat-y2k -Winit-self -Wignored-qualifiers -Wold-style-declaration -Wold-style-definition -Wtype-limits -fstack-protector-strong -I/usr/include/p11-kit-1    -I/usr/include/libpng16 -I/usr/include/spice-server -I/usr/include/cacard -I/usr/include/nss -I/usr/include/nspr -I/usr/include/glib-2.0 -I/usr/lib64/glib-2.0/include -I/usr/include/pixman-1 -I/usr/include/spice-1 -I/usr/include/cacard -I/usr/include/nss -I/usr/include/nspr -I/usr/include/glib-2.0 -I/usr/lib64/glib-2.0/include -I/usr/include/libusb-1.0
LDFLAGS           -Wl,--warn-common -Wl,-z,relro -Wl,-z,now -pie -m64 -g -L/usr/lib64
make              make
install           install
python            python -B
smbd              /usr/sbin/smbd
module support    no
host CPU          x86_64
host big endian   no
target list       x86_64-softmmu i386-softmmu
tcg debug enabled yes
gprof enabled     no
sparse enabled    no
strip binaries    no
profiler          no
static build      no
pixman            system
SDL support       yes
GTK support       yes
GTK GL support    no
GNUTLS support    yes
GNUTLS hash       yes
GNUTLS rnd        yes
libgcrypt         no
libgcrypt kdf     no
nettle            yes (3.2)
nettle kdf        yes
libtasn1          yes
VTE support       yes
curses support    yes
virgl support     no
curl support      yes
mingw32 support   no
Audio drivers     oss
Block whitelist (rw) 
Block whitelist (ro) 
VirtFS support    yes
VNC support       yes
VNC SASL support  yes
VNC JPEG support  yes
VNC PNG support   yes
xen support       no
brlapi support    no
bluez  support    no
Documentation     yes
PIE               yes
vde support       no
netmap support    no
Linux AIO support yes
ATTR/XATTR support yes
Install blobs     yes
KVM support       yes
RDMA support      no
TCG interpreter   no
fdt support       yes
preadv support    yes
fdatasync         yes
madvise           yes
posix_madvise     yes
sigev_thread_id   yes
uuid support      yes
libcap-ng support yes
vhost-net support yes
vhost-scsi support yes
Trace backends    log
spice support     yes (0.12.10/0.12.6)
rbd support       no
xfsctl support    yes
smartcard support yes
libusb            yes
usb net redir     no
OpenGL support    yes
OpenGL dmabufs    yes
libiscsi support  yes
libnfs support    no
build guest agent yes
QGA VSS support   no
QGA w32 disk info no
QGA MSI support   no
seccomp support   no
coroutine backend ucontext
coroutine pool    yes
GlusterFS support yes
Archipelago support no
gcov              gcov
gcov enabled      no
TPM support       yes
libssh2 support   yes
TPM passthrough   yes
QOM debugging     yes
vhdx              yes
lzo support       yes
snappy support    no
bzip2 support     yes
NUMA host support no
tcmalloc support  no
jemalloc support  no
avx2 optimization yes

I'm going to try and put the VM on an EXT4 partition and see if I can duplicate the issue.  It might be related to ZFS.