When your forum post limit 20 per-page. You willing to post in the same page for 21st post, you have ad_message_below with adsense, it will interrupt into white page or adsense ads only when you posted it. If you refresh it, it will be fine.
This is a bug or just problem with adsense interruption ?
NB: This problem only happen with ad_message_below and ad_message_body including on Conversations page