I've had the same problem with the event-limit as well...

I think it's the mass of the events that counts,since I could play a level that had hurt events ALL OVER the tileset(I used some weird event-replacement trick to replace all not-used tiles into a certain event),but the limit on trig.rocks usable is limited...
Meaning
-hurt event:not visible
-trig.rock:alot of mass(almost 3x3 tiles)