Can't create newlines in text field for some forms

The helpdesk software I use, UserScape's HelpSpot, uses the TinyMCE text editor control to compose responses to support requests. I've begun to use it as an embedded webpage in RDM (would love to use Chrome or even Firefox with it embedded but that's another request, one I've already made :-)

The problem is that when typing a response in the form using RDM, pressing Enter doesn't do anything. So I can only type one line of text, and can't start a second paragraph or add a signature to the response. This works fine in IE (8, on Win7 64-bit RTM) directly, just not when it's embedded in RDM. I was able to also replicated the problem by logging into my WordPress administration area (on my self-hosted WordPress blog), which also uses the TinyMCE rich text editor, and the same problem exists there (I imagine this would also reproduce with a free WordPress.com blog or any other self-hosted install; I'd be happy to provide credentials to a WP site for testing if needed--much easier than using our internal helpdesk!).

What happens is the Enter key just does nothing. The cursor just sits where it is and blinks as usual. It's as if I were typing this post and everything worked except I couldn't create a new line or paragraph.

It seems (although I haven't extensively tested) that a "normal" textarea form field works correctly when embedded when you press Enter, and so far it's just TinyMCE editor boxes (across tools) that cause issues. (And I'm pretty sure that HelpSpot uses TinyMCE but not 100%--the fact that WordPress creates the same issue seems to confirm this however as I know it's what they use.)

Additionally, I also get a Script Error (JavaScript) when loading the WordPress New Post page in an embedded window, whereas the same page is fine with no warnings popping up in IE directly.

This is in the current Beta, 5.6.0.15.