Here is a breakdown of exactly what is broken:
It cannot be fixed except by a client hotfix. It is not an issue caused by addons, nor is it an issue in the lua interface code, but rather a bug in the C code that is not setting the final form ID and sending a shapeshift event to tell the lua interface. The bug appears to only happen when powershifting (shapeshifting from a form to the same form, ex. using a /cast !Any Form macro)
Unfortunately using powershift macros is the bread and butter of cat dps in TBC.