Ah, so it was a bug after all! Maybe it's time I tried using the Updated SDK... I just found out about
this issue, if the problem is related to that then Updated should have fixed it. I'll try to finish my map(s) first though.
EDIT: For the record, I revisited the c4a1 portal room, and there they are - I remember now that I did these sprites in game before, I even looked for them in the map source, and thought it was weird when I couldn't find them...
About 5 plantlight sprites crowded in the same spot
And, as it turns out, the spot they appear in is the world origin, or next to it.
scientist/asexpected.wav
The oddest thing is how this bug seems to not place the sprites
exactly at the origin. In my map the plantlight sprite isn't there (probably at a random out-of-bounds location next to it instead), but random sparks do appear at the exact spot sometimes. Well, at least it's fixed in Updated.