It automatically fixes itself after reloading, but the icons remain disabled otherwise. Mentioned on Curse.

Steps to undertake:

• Change GUI to re-enable elements that could potentially be disabled, so that they won't stay disabled forever if it happened at some point
• Change GUI to account for accidental 0 return values of the spec functions (to avoid this issue being a problem)
• Fix any other part of the addon that relies on GetNumSpecializations() or GetSpecialization(), and potentially other related APIs, as they are prone to return invalid values temporarily, which might cause issues that haven't been discovered yet (see Edit)

Edit: I can't say for sure if the other calls to the same API could cause issues, but at least they don't disable any GUI elements permanently. Considering this fixed until further notice.