I'm not sure what the logic is, or whether this is intentional, but I noticed that we might be removing tags incorrectly. In task T228851, I see several retagging actions which are probably related to different patches. At one point, I tried to fool the bot by deploying a patch via a SWAT and the bot very impressively removed the expected, scheduled deployment tag, adding the earlier version. However, when we linked an additional patch to the task, the bot removed the earlier tag and added the later tag, again.
I think the correct behavior is to reprocess all linked patches, each time there is a change which might affect where they might be deployed. The tags should be unioned, and then any stale tags removed.
Finally: thank you for this helpful tool!