<event type="string" description="Decides on what event the description triggers" options="static,rollover,imageinfo_button">imageinfo_button</event>
It seems like there was a missing setting in 'text1' module that was only available in 'text2' in the themes. I have now added the option "imageinfo_button" to the text event options, so that you may apply a descripton-text to display only when rolling over a description button in imagebuttons.
Either wait for update, or use <text2> module which has this option already. Am I making sense?
You seem to have progressed correctly by enabling the imageinfo button, but then you also need to enable one of the 'textmodules' to trigger on the imageinfo_button event using the setting above.
Just to comment your discussion also ... I think this may be what you are looking for, although it will not be an option to add this button to another location(f.ex. bottom right of image, unless you want to move ALL imagebuttons there). We need to keep items grouped to keep some order. We could integrate an option to have the imageinfo_button also as an option in the maincontrols.