Re-installing won't fix it. It's in the code.
Apparently most of the Hide function was removed or disabled when MC6 was being distilled from X1, but a bit of code was left accessible through what should have been an unsupported keystroke.
This won't fix MC6, but I would suggest the same thing Beagle mentioned in the other thread.
Did you get X1LE bundled with the Quad Capture?
If so, install it. Having both programs installed won't hurt anything. You should be able to open your MC6 project in X1LE, and unhide the tracks there.
All of your plug-ins will be available to both programs, so you can continue working in X1LE, or save the project, and open it in MC6.