When you try to use a brush or pixel brush with 1px size on a layer which has been stretched to 800%, brush becomes unusable.
steps to reproduce
create new RGB/8 document, size XGA
add a pixel layer
use brush and pixel brush, select smallest 1px sized basic hard brush. Make a few strokes to check it works.
add rectangular shape, 8x8 px. Fill with grey.
rasterize rectangle
use transform panel to stretch by factor 8
try to use pixel brush or brush using touch gestures. Use different color. Only <10% of strokes show effect, most get „rejected“.
FullSizeRender.MOV