Avant que always takes the subjunctive, whether there is a change in subject or not. Note, that this isn't in contradiction to your rules.
-- Chris (not a native speaker).
I was taught at school that Avant que takes subjunctive only when there is a change of subject.
This is also confirmed here:
However, it seems that in the examples on this website, Avant que always takes the subjunctive, regardless of whether there is a change in subject.
For example: Avant que je n'aille chez Paula, je dois acheter des fleurs.
(Before I go to Paula's, I have to get some flowers)
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