The messages were only freed on error.
==12== 1,100 bytes in 1 blocks are definitely lost in loss record 698 of 729
==12== by 0x4E98C22: virBufferAsprintf (virbuffer.c:294)
==12== by 0x12C950: vshOutputLogFile (virsh.c:2440)
==12== by 0x12880B: vshError (virsh.c:2254)
==12== by 0x131957: vshCommandOptDomainBy (virsh-domain.c:109)
==12== by 0x14253E: cmdStart (virsh-domain.c:3333)
https://bugzilla.redhat.com/show_bug.cgi?id=1001536