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It's the same in all countries with not-clear borders. Applies to eg Georgia, Serbia/Kosovo and India/Pakistan too.

Interesting, even Spain seems to not get a red outline (maybe because of Catalonia?)

It could be, but searching for Catalonia in Google maps explicitly indicates it's a part of Spain.

Another explanation would be the dispute with Morocco about Perejil Island:

Or even the dispute regarding Gibraltar with Britain.

Or the disputed border with Portugal at Olivença/Olivenza.