I see that TwoPynts chimed in with,

It is not a bug per se.

Whether you call it a bug or not, it is fixable.  The software has to be written
to count the number of messages that are visible to the current user. 
Applying that enhancement will make the page breaks consistent. 

For administrative reasons deleted comments remain in a thread invisibly.

i.e., "Pay no attention to the man behind the green curtain". 

Ha, Ha ... Perhaps not ... but now all of us know that they are there. 

Once upon a time, I saw a SIG that explained it as ...

 ~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-
I saw no one, but I knew they were there.
It was not paranoia, just a reasonable deduction.
Unless, of course, that was what they wanted me to think ...
~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-

Comments???

--
Martin