I have found the Geovents and burning Trees both contribute massively to the total particle-count of Spring, resulting in un-necessary culling of particle FX generated through custom ExplosionGenerators. This is no big deal for fast explosions, but it means that slow, large-scale ones suffer from rapid cut-out of the particles in the middle of the animation. I think that those two sources of particles should not contribute to the total particle-count, because even a few Geovents = hundreds of particles per second.
Even weirder... those particles don't seem to be getting culled from the World. I have been able to get them to show up again, by .give-ing the object I just self-d'd again- the ones that were culled start drawing again, like nothing happened. Very weird.
Just thought everybody should know about this, as it means that a certain super-FX I'm working on... ain't quite so super on maps with trees or geos

[BIG, FAT EDIT]
No, the problem is even worse than I thought. It even happens on maps without any of these Features. I just hadn't tested it thoroughly enough
