Hey, big sorry for not responding any earlier, some weird flu kept me away from keyboard in these last few days, to be honest. Sorry!
Yeah, fortunately we are aware of this problem and are really close with our latest update that will take care of these problems our old thumbnailer is causing. We sincerely hope this one will roll out before the end of this week, but since there are still some minor (but crucial) updates to be finished, we really cannot make any promises.
But you have my word we are working hard on it! Thanks for your heads up and continuous patience — we really do appreciate it!
In the meantime — you can download and install the previous version of our plugin, which handled your thumbnails much better. You can get it under our developers tab, on the plugin page. Here's the link: http://wordpress.org/plugins/wordpress-23-related-posts-plugin/developers/
Let me know how it goes or if you have any more questions — I'll gladly help!
Take care & have a nice day!