This type of question has always caused issues like this as it is a fuel related question but not fuel policy directly.
It's really a light aircraft fuel question where a reserve of REMAINING trip is perfectly okay, though strange to get your head around especially landing in THEORY with no reserve, but of course you started with that 25% and assuming nothing happened then that reserve would be intact on landing.
Questions similar to this have never mentioned FINAL RESERVE as I should agree with you if it did. Trust me with years of instructing experience and knowing what the examiners are after this is a proportion question not fuel policy knowledge, though perhaps not the best way to test it by ignoring the "rules". The examiners are basically saying with inaccurate fuel gauges the reserve is set at 25%, you don't know how that is split.