I'm the original reporter of this problem and would like to add a possibly helpful detail. I did wireshark traces and found that in the failing case the length of the group name in the SETATTR call is given wrongly:
Opcode: SETATTR (34) stateid [StateID Hash: 0xafa9] seqid: 0x00000000 Data: 000000000000000000000000 obj_attributes attrmask recc_attr: FATTR4_OWNER_GROUP (37) fattr4_owner_group: <email address hidden> length: 25
In the working case the length is given correctly as 24 (the actual group name has the same length as "<email address hidden>").
I'm the original reporter of this problem and would like to add a possibly
helpful detail. I did wireshark traces and found that in the failing
case the length of the group name in the SETATTR call is given wrongly:
Opcode: SETATTR (34) 000000000
recc_ attr: FATTR4_OWNER_GROUP (37)
fattr4_ owner_group: <email address hidden>
length: 25
stateid
[StateID Hash: 0xafa9]
seqid: 0x00000000
Data: 000000000000000
obj_attributes
attrmask
In the working case the length is given correctly as 24 (the actual
group name has the same length as "<email address hidden>").