GAWK implementation (source code) question (change noticed in 3.1.4)

The question has to do with the (new?) type Node_var_new.

I'm curious as to when this type was added and what its purpose is.
I had made some modifications to gawk in earlier versions (maybe 3.0.6) and
did not have to deal with this, but now I tried making the same mods to
3.1.4 and found that if type is Node_var_new, you have to change it to
Node_var - after which all is as before.  Can anyone tell me why this
change was made?