what's so special about POP filters that they can be lost so easily?

KMail on KDE 4.6.5

This morning KMail gagged on something and had to be terminated.

When starting up again my POP filters were lost. Nothing else.

Disappearing POP filters have been an issue from way back in KDE 3 days.

What's so special about these filters that they can get lost on a crash 
when I've never lost anything else except from mark-as-Read tags? I filed a 
bug report years ago on this, and it appeared to be solved, but apparently 
not. 

Just POP filters are lost from kmailrc, sections like this:

[PopFilter #0]
action=down
contentsA=0
fieldA=<size>
funcA=greater
name=<<size>>: 0
operator=and
rules=1

and the value of

[General]
popfilters=0


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