Maybe the converting a ved-file from one version to another could be a reason for mistakes. I have built a game f.e. in 4.25, then I go to 5.0, to 5 RC, then to 5.05, to 5.09, now 5.1.
The second reason maybe the switching from one to another Lua version which has little, but noticeable changings.
And the biggest one is the reconstruction of the whole engine to 64 bit with new logics, new editor elements and new features. So: It matures with the customer....