Richard Stallman wrote:

>	      if (! interval_has_some_properties_list (properties, i))
>    ! 	    if (modified)
>    ! 	      {
>    ! 		if (BUFFERP (object))
>    ! 		  signal_after_change (XINT (start), XINT (end) - XINT (start),
>    ! 				       XINT (end) - XINT (start));
>
>I'm not confident about that code.  It runs the after-change hook, but
>in this case, where is the before-change hook run?
>  
>
The before-change-functions are run by modify_region called immediately
before the changes are done by remove_properties.
Actually, I have changed that part of the code a bit to make it more
readable, see the attached patch.

The general idea is:
Fremove_list_of_text_properties has a for (;;) loop that loops over the
parts of the interval. It updates the flag `modified' recording if
changes have been done. To make things work right, we must call
modify_region before calling remove_properties iff modified == 0, and we
must call signal_after_change before returning iff modified != 0.