exported TyCache doesn't match the flow sim

[john.zi]

Hi, so I've been struggling with this issue for a while now and it give me a real headache.  I am simulating some grains plus spawning some extra sand from them using property Test (Diff mag). In general when I got to the point that I am happy with the results in the viewport I am trying to export it to TyCache or PRT. Unfortunately the caches which I am generating doesn't look the same as the sim in the viewport. I get bunch of random particles floating and going upwards like there is no gravity. In this example below maybe there are not that many of then but when I significantly increase the number of grains the difference is more striking. 
Also I've noticed when I disable Property Test (Diff mag ) where I spawning new particles, then Tycache is more consistent with what I see in the viewport. 
I was trying to cull those particles using the volume but I guess there must be another way that I am not aware of. Did anybody experience anything like this I know how to solve it? 

Thanks !