I've been having this issue too. everything under -tools is broken, can't save particles, can't save commentaries and you can't save the materials either.
in short, -tools seems to be broken since steampipe
so in the meantime, check out vide
http://www.riintouge.com/VIDE/
This thing has a particle editor but it wont render them in real time for you. So find settings you like in the tools mode and enter those settings into vide. That's about as good as it gets at the moment. I've been meaning to write to valve about this but w/e
and to anwser lampenpam, the thing just exits to desktop, the game doesn't freeze or anything, it just quits without warning, and your work is not saved
I guess you can try messing around with the particle editor of other games that have not been steampiped but I think all of those are using a different version of pcf (
https://developer.valvesoftware.com/wiki/PCF_File_Format)