I've been writing some (very dodgy) DMA related tests and I've come across a situation that has different results to hardware: dma_mode3.zip this ROM is a broken implementation of DMA.

The L and R buttons will cycle the colour value used for the DMA.

The DMA uses channel 0 to fill a single 16bit colour into VRAM 0x06000000 from a single copy source in IWRAM 0x03007EDC. The DMA control is 0x01009600.

This happens for me with all DMA channels in pretty much all permutations of DMA you can think of.

This is what mGBA displays:

Versus hardware:

Here's VisualBoyAdvance-M's result: