Or, it could be a setting in another folder (In BAIN folder likely) that does not revert.
I'd hang in there for an update but if impatient you probably could go in and delete all Wrye Bash files in your Oblivion folder then reinstall 287 and if then the problem persists take a more drastic measure and delete (or rename or move) the bash folders in the BAIN directory and re-initialize the installers tab again with 287 installed. Doing that all packages will be seen as uninstalled but a quick reinstalling them should then return functionality.
That is my best guess and I take no responsibility if it does not work.
I renamed the Mopy, Bash Patches, and Ini tweaks folders, installed 287, and still have the inability to uninstall or install rars.
By BAIN directory do you mean the bash installers/mod data folders?