There are cases with tons of overlay mockups hidden

[5argon]

Normally I set the hide flags as hidden so you don't see it, plus an "active" one is only a single instance so it doesn't look like this bug exist. By removing the hide from hide flags, it is revealed that sometimes the old existing instance was not reused and a new one is created in its place. This occur frequently on recompilation. While it doesn't affect workflow and they will all go away together because of DontSave, it should be fixed anyways.