Created attachment 104469 [details] Example stamp vs brush stroke When used, any brushstroke made with an animated brush tip set to random mode will always start with the first frame of the brush tip. When you use the brush as a stamp, it makes it so you can't benefit from the randomness. Also, if your preset has a large spacing, even with multiple brushstrokes, the repetition soon becomes visible.
It's actually another problem: the first tip is always in wrong mode i.e. first "random" tip won't work as random and first "pressure" won't work as pressure dynamic tip. This happens every time you change mode. You have to create second tip to make it work as supposed.
I can confirm this... I recall there being another bugreport with this issue, but it seems to have been closed?
I had some experience in creating brush tips. When I chose random option, brush uses tip's layers sequentially, but after it if I create brush tip with incremental option, created brush is random. Sadly, this doesn't work when I use incremental option first time when creating brush - it is not random. It will work as intended, when I create random brush and then another brush with incremental option.
Random brush tips should be painting correctly now in 4.0 DoubleDee is talking about a separate issue than what GDquest mentioned. Theirs relates to brush tip creation. Wolthera just did a patch for that to fix the random/sequential saving. It will be in 4.0 as well. If there are additional issues with this a new ticket can be opened up.