I bet it's because the xml format was recently changed: now all input types are listed for each game, not just one.
Example:
Disc of Tron
used to list one input control: trackball
now lists three input controls: 8-way, dial, & trackball
IIRC, mamewah needs to use the old listinfo format, which can only list one input, & the current xml2info.exe can't translate the multiple inputs and outputs "none" for everthing instead. Krick posted an xslt file somehere on this forum that does the translation better. (Use it instead of xml2info if you still use xml2info.)
And, still IIRC, minwah is trying to make changes so mamewah can directly read listxml file. So wait a little, hopefully, and update when it comes out.
(I don't use mamewah, so grain of salt.)