Say that you had a text buffer, and hooked up a ::insert-text handler so
that for every a typed in the buffer, you inserted a non-editable
b after it.

 (Saby thabt you habd ab text buffer abd ..)

And then you wanted to hook up a ::delete-range handler so that when
an a was deleted, you deleted the b.

Right now, what happens is that this confuses the logic in delete_interactive()

Say the user deletes the range:

 [Saby] that you

First ::delete-range is called for [Sa]. The ::delete-range handler
deletes the text, and the following b, so the next segment to process
is [y]. But delete interactive is hardcoded to think that after it's
called ::delete-range, the next segment is not-editable (it's assuming
that ::delete-range doesn't affect the alternation of editable and
non-editable.)

I'll attach a patch to fix this by simply requerying for the editable
status after each call to ::delete-range.