Yeah I think it stacks with your settings, my server has 50x hatch & 30x mature, I got impregnated by a reaper earlier and the pregnancy should've been 14 mins but only took 4 which is 150x hatch so it's stacking with the 3x, tested some things in SP yesterday and they were fine but I think I have events disabled in launch options
Seems to have been a thing since the Christmas event, can't remember having to adjust my settings for any events before then
The Valentine's event was one of the first ones to use the active event system. When that one was set up the multipliers were hardcoded (I believe it predated the newer dynamic config) so it was pretty much the only event that did rates this way (and it never will again)