What specifically did 1.6 change scripting-wise to cause mod CTDs?

[Zinthros]

So since 1.6 official (all of these were tested alone, none occurred with the beta):

 

Natural Skyrim Rain causes save-game baked CTDs you can never get rid of.

Sounds of Skyrim causes severe geometry loading errors outdoors (especially during the opening scene -- Helgen's walls are missing).

Moonpath to Elseweyr causes periodic CTDs (fixed in Moonpath 0.92 or 0.93).

Winterhold Destruction Ruins causes periodic CTDs (fixed in an update there as well).

and Tales of Lycanthropy causes save-game baked CTDs you can never get of.

 

What specifically did Bethesda change scripting-wise from 1.6 beta to 1.6 release that causes this? Lower error / flimsy scripting tolerance?