I'd be interested in you posting the complete code... not just the button and variants.
For instance, I've seen an eventhandler get attached to the main xp:view tag by accident. That has broken buttons from working.
That's all I can think of at the moment. You say nothing is written to the log... which to me imply's the server console log.nsf. The other thing to make sure to check is to go into debug mode on your browser and see if there's anything showing in that log. An unexpected error there could break buttons from working.
Good Luck