In the V6 WIP build that went out Tuesday, July 28, there is a major bug in these two commands, and it may affect some others. If you split or trim a surface with more than one curve, and those curves intersect on the interior of the surface, the commands will ignore the intersecting curves. This happens even if the curves meet only at their ends. Single curves with kinks will also be rejected since they get split up before the bad code is called. It seems that if the surface is a part of a polysurface there is no problem.
I’ve already fixed the problem, but I don’t think we can put out another build until the weekly build on August 4. Sorry about that.