One "hole" in each scan line to turn off blitter nasty?
 

Came across something today that I hadn't heard before.

Apparently there is one DMA slot per scan line that can't be used by the blitter under any circumstances. It was suggested that this was done to allow the CPU to turn off blitter-nasty if necessary.

Anyone know anything about this?

Not true. Can't be true :)

It would break lots of demos that do not wait for the blitter and use blit that does not have any free DMA slots. (Usually D=A copy)

Perhaps it meant Copper? Copper can't use last slot (AFAIK only if PAL mode).