I think it's this part :

https://github.com/espeak-ng/espeak-ng/blob/f4c2ad3b7f3c29b40cd6029c5f82f2ba1156fff7/src/libespeak-ng/compiledata.c#L790-L801

Line 798 will modify the character. I tried to invert the last line, but pushing back the ')' will result now in an infinite loop. I guess pushing back a space was a trick to get rid of the parsing of the ')'.