Bug: undeletable section in a document

Hi,

I'd like to report this bug, which I've been observing occasionally.
Sometimes, it is not possible to delete a selected region containing
MathML. I attach an example. The problem appears to depend on the
relationship between the undeletable region and the rest of the
document.

I say this because in the case of this example, if one copies and pastes
the undeletable region into a new blank document, it is possible to
delete it in the new document. So its undeletability appears to be
connected with other parts of the document. Furthermore, other regions
of this example document are deletable. Also, slightly changing the
extent of the selected region makes it deletable. Thus I attach the
entire document, rather than just the undeletable region.

OK here is the example. Open the attachment in Amaya and select the
region between:
"Bell states:"
and
"If <lambda> is unknown, the probability distribution"
*inclusive*.

You should find that hitting backspace or delete or selecting the Delete
menu item has no effect.  If I enlarge the extent of the selection, say
to include sections 4.1.1, 4.1.2, and 4.1.5, I can delete it fine.

This problem has been a nuisance for me before, as it has resulted in me
having to delete more than I want to in order to delete something!

Thanks,
Joe