Hm. I think I discovered the source of the fixed random seed bug (or Deforged feature) in Lua maps. Maybe it was already known by someone, but it's new to me. Still verifying if this is a real discovery.
The seed gets reset to fixed after every test map run (I think the fixed seed code runs on client closure). If you open up preferences, toggle it on and off, then click Okay and run test map, the seed is properly unfixed and pseudo random again [edit] as long as the randomseed is fixed to a timer.
Essentially, it has to be "re-toggled" every run of test map.
edit: as a side note, I do this in conjunction with a new math.randomseed()
edit 2: take with grain of salt, testing some things to verify