Line height rendering issue with RET or TLF?

I've been developing quite a complex Flex App for a client using a lot of the functionality offered by TLF and the Rich Editable Text flex component.

The app enables Maths authors to write questions like the one shown in the attached screengrabs.

In the grabs you can see an issue which occurs infrequently but still occurs in the latest Flex SDK that I've just updated the app to (4.0.0.9948).

The issue is in the instance of the RichEditableText component that displays the question. The first line of text seems to be getting overlaid by the second (perhaps the line height is being incorrectly measured by the TLF).

The font used is embedded in the CSS.

The second grab shows the focus on the text when highlighted. You can see that's incorrect too. Presumably this is related?

I will try to put together a simplified project that reproduces the app but I thought I'd raise it here first to see if this is a known issue and whether there's a work around?

Thanks

Nick