Last year when my laptop died in September, I lost all my old Qrack source codes so I don't quite have the ability to backtrace through the versions.
If I recall, the historical issue with Qrack coronas is that they specifically would appear through world entities (doors, the fake start map floor) so I am guessing they used vis.
Without knowing, I'm going to guess you used the traceline that the QMB particle stuff uses that also collides against ... ugh ... I can't remember what it also collides against ... but it was an improved traceline of some sort. QMB particles have to collide with everything and use an enhanced traceline that isn't quite the same as the standard traceline, but it has been 9 months since I've thought about what makes it different (because it was crashing my engine at one point ... well not directly, but it wasn't fond of being connected to a server without the map ).
/A somewhat crappy quality post, but then again I'm trying to aggressively attack my "to-do" list