Changing order of stages works but always causes error message

Dragging a stage up or down in my list of plan stages gives this error:

Stage move failed
Failed to move Stage, the provided Stage (PurgeExpiredBuilds) is not currently part of the Plan (NAMOB-TCANDV0102RL)

The stage is properly moved, may or may not reflect its new location on the web page, but reloading page always shows that the move succeeded.

This occurs in Bamboo version 4.4.4, which I can't select in the "Affects Version/s" dropdown on this site. I chose 4.4.3 instead, but I don't really know if the bug exists there.