Random glitches in various games with Twin Famicom AN-505-BK

[timherr]

I'm experiencing strange behavior with my FDSKey when using on a Twin Famicom AN-505-BK. Behavior varies, depending on the game:

1. Some games work fine
2. Some games get stuck in a boot loop, constantly showing the copyright screen, then punting back to the BIOS screen and re-loading the disk
3. Some games freeze after loading (e.g., Bubble Bobble will freeze just as the first level intro animation is about to end)
4. Some games exhibit odd behavior (e.g., I get stuck at Dead Zone's name entry screen because the "END" button's entry becomes a backspace, and the backspace button enters the katakana ウ-symbol)

This all happens consistently when connected to the Twin Famicom via an adapter cable. The above behaviors even occur if I write to a physical disk via the FDSKey and DupliFDS. All of this happens with both the 1.3 firmware and the latest interim firmware. Changing the rewind speed makes no difference. Reformatting or changing SD cards doesn't help

All of the above behavior does NOT occur if I connect via a RAM Adapter cartridge (still using the same Twin Famicom). So it seems to be something specific to using the Twin Famicom adapter cable.

I haven't been able to rule out a bad adapter cable (I purchased one from AliExpress), but continuity checks tone out correctly based on the wiring diagram on the project homepage.