It likely is a Windows / Mac (and/or browser? -ie. if using Safari) issue ... vBulletin is developed and tested by mostly Windows-based folks; optimized for MSIE.

With that said ... here are two things to try...

* Instead of using the Quick Reply window at the bottom, click "Go Advanced" and then enter your reply.

--- if no good, then try...

* Click on the "Quote" button of the message you're replying to, delete out all the quoted text if so desired, and then enter your reply.

One of the above approaches may work.

Ron