I removed my previous comment. b4n probably had his reasons to make spawn-Win32 unicode, and it's not my job as a current non-developer to complain anyway. I asked him to state his name as a developer of the unicode part, and that's it.
Now, it'll be interesting whether a callback that detects continuous empty G_IO_IN-s can add a timeout source to the context (removing it's own gio watch source is easy), and whether G_IO_OUT-s are affected too...