Ah, this manga. Always concerned with yuri and uri-nation.
I really like this development, though -- as others have observed the gender bender element is kinda subdued given how feminine Mahiro naturally is now. There needed to be something to bring it back to the fore.
I think urination based accidents are just here to stay. Either the author has a kink and insists on including it, or they're trying to manipulate the content of doujins drawn about this for the lulz. Possibly some variation of both.