It has everything to do with it.
The only issue with breaking backward compatibility is if someone overwrote the MODE command with their own /mode alias, expecting it to fallback instead of recur.
In any other case where it's not a built-in command, the current behavior is to raise an error "no such command." A change that avoids an error can't be considered as breaking compatibility.
They SHOULD be using !mode when overwriting a command if it shouldn't recur.
mode { !mode ... }
The help file is very clear that you should use the '!' prefix if you do not want it to be processed as an alias. The current fallback behavior is just coincidental since the removal of recursive abilities. Breaking this fallback behavior shouldn't be considered breaking compatibility, because it's invalid usage according to documentation.
