Just want to update to let you know this is a general problem with other plugins like TinyMCE Advanced also. With that plugin the button is there but opens up with the TinyMCE Advanced table popup. As soon as I deactivate TinyMCE Advance your plugin takes over the table-button again.
And as vjargiro said, in Ultimate TinyMCE the table button doesnt work at all and only your button.
Have you thought about creating your own button? I have TinyMCE Templates also and that plugin adds its own button instead of hijacking another button. IMHO it would be better to leave the regular table-button alone or at least let us choose.
I love the plugin so I really do want to use it but need a proper table-button function also for those tables that doesnt work well in the plugin.