Indeed strange, it seems that something does not catch the fact that the user request is a postback, or a form post... And it reloads thus the file from the cache without processing the ASPX.

I don't know much about DNN caching, so I can't really help you in some way other then you already did  (disabling the cache  :-)) I should test that, to see what happens  :-)

Thinking about it, shouldn't this be expected behaviour. You would expect your controls to be cached when your module is being used. Maybe you should always have cache set for the module as zero when under development, and put this back to normal when you build it for release? Comments?