I just discovered this: In Nullpomino's Gem Mania (simulates TGM3's Sakura mode), if you hold up and left together for about 1 second, the stage is automatically skipped with a 30 second time penalty, and the "evil laugh" sound effect when the stage timer runs out is played. Is this supposed to happen? I found it by accident when attempting to use autocharge DAS and hard drop at the same time, causing me to unintentionally skip several stages. I've played Gem Mania many, many times and this has never happened before.
Sounds like a weird key ghosting thing. If you hold whatever you mapped to input F, you can initiate a stage skip. F acts like the Start button would in TGM modes -- speeding up the Grade Mania 1 credits, skipping stages in Gem Mania, etc..
Found the problem out: I had mapped left and F to the same key. Thanks! I had no idea what the F button did until now.
