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There is a bug in the control of the Original Game Boy game Gamera - Daikaijuu Kuuchuu Kessen (Japan) (SGB Enhanced) that I first discovered in version 0.7.3 and it varies depending on the version. It happens with both the translated ROM and the original from No-Intro set.
In 0.7.3 stable: Select doesn't work and I can't continue the game because in a later screen I'm asked to press it obligatory.
From 0.8.0 to 0.9.1 stable: None of the keys work, or Start doesn't work (I don't know how to tell). The game starts but as it asks to press Start I can't continue. This also happens in the latest dev build 0.10-7010-a507276e2 from 05-30-2021.
An interesting thing is this game does not write $30 to joyp between the player reads! It only does it once after both players are read out. This seems to imply that the docs saying that writing $30 to joyp to increment the player count is wrong. This might be the source of the bug.
I wrote a few testroms to test my theory (you probably saw them talked about in #research on gbdev), and my theory seems to be right. Writing $30 is unneeded to increment the joypad number. In fact, the tests seem to indicate that a simple P15 low to high will increment the joypad number (implementing such behavior still passes previous SGB tests anyways).