Leftover VBDs
A regression in VM.revert was introduced in xapi-26.1.4-3.3 and fixed in xapi-26.1.11-1.3. The bug left VBDs attached to the VM when they are not present in the reverted-to snapshot (instead of destroying such VBDs, as done before the issue was introduced and after the fix).
VDI.snapshot_of issues
A race condition during VM.revert could inadvertently corrupt the snapshot_of field of other VDI objects. XAPI received a fix for this issue in the version xapi-26.1.21-1.1, but the fallout from previously corrupted database entries can lead to issues, since some API users can then interpret the non-snapshot VDI as if it was a snapshot VDI. A helper script is provided to fix xapi databases with incongruent snapshot metadata.