Solved: SetCurInstType / GetCurInstType problem - not working as expected
This will hopefully save some time to someone who might encounter the same problem as me:

I used InstType for conditional section execution; there's no components page but I find the method more elegant than using variables. The problem occurs when you have two or more identical insttypes, in terms of associated sections. In my script, I had two insttypes that ran the same sections but were different globally (some pages are skipped with one but not with the other). If those insttypes are e.g. 3 and 4 and you use SetCurInstType 4, GetCurInstType will return 3. Trying to figure out what's wrong with my script drove me mad, before I realized they're internally treated as a single insttype and it's impossible to set it to 4. And the solution is simply to assign an additional blank section to one of them.