Currently viewtopic_body_post_buttons_after / viewtopic_body_post_buttons_before template events are placed within the condition

<!-- IF not S_IS_BOT -->

			<!-- IF postrow.U_EDIT or postrow.U_DELETE or postrow.U_REPORT or postrow.U_WARN or postrow.U_INFO or postrow.U_QUOTE -->

Thus, there're cases when user is unable to see custom buttons which don't depend on conditions mentioned above, as well as unable to add a custom button with its own condition (alike build-in post buttons).
The decision would be adding another events outside of those conditions to allow ext authors creating their own 'independent' post buttons list.

This issue is prosilver-only, as in subsilver2 original events aren't wrapped with the conditions.