RichTextCtrl issue

Before upgrading to a RichTextCtrl, I had two widgets in my
application -- a TreeCtrl, and a TextCtrl. When focus was on the
TextCtrl and I hit enter, a newline would be inserted in the text
area, as expected. Nowhere in my application do I intercept the
natural functionality of the Enter key.

I've now changed that TextCtrl to a RichTextCtrl -- that's the only
change I've made. My code runs, but there's an issue. When I hit enter
with focus on the RichTextCtrl, focus switches to the TreeCtrl instead
of entering a newline. Basically, I can't insert newlines with the
Enter key.

How can I resolve this issue? Thanks!