Particle/Mesh collision doesn't work in BP


A rather strange phenomenon I recently experienced:
I created a hollow sphere using BSP brushes, then converted it to a static mesh.
I then took a sort of a water particle I had, added an Actor Collision module to it & made a few tweaks.

Now, here’s the strange thing; I dragged a hollow sphere static mesh into the world, gave it a Glass material to be able to see through it, and added two emitters of that Water particle inside the sphere.
I messed around with the locations & scale, till I sorta got the effect I was looking for (the hollow sphere filling with ‘bouncy’ water particles).
When I tried to turn this whole thing into a blueprint - the whole collision behavior seems to stop working - the water particles go straight down, ignoring the sphere altogether
(see attached image - left side is in the world, right side is as a blueprint - but behaves the same when dragged into the world).

Is there some limitation I’m not aware of that prevents this behavior from being included as part of a blueprint?
(I made sure Collision settings haven’t changed, & that it’s both in the editor & in simulate/play).
What am I missing here?