... usually with Sonar 8.53 imported files ... after working 'awhile' on said imported files.
 
1) I have not been able to 'trigger' the bug nor duplicate it.  
 
2) It happens when I've 'played' in prochannel, iirc.
 
3) I realize its not wise to import 8.53 files but I have to.
 
4) (X3d doesn't state the bug is fixed)
 
Any thoughts are appreciated as this bug is frustrating.

So...
Does just to confirm this doesn't happen with new X3C projects?
Once in X3C try saving as bundle, and then saving a project.
Maybe try copying/pasting the channel into a brand new project to see if you have the same issues.
 
Otherwise I would certainly checkout X3D, just because it isn't documented doesn't mean it isn't fixed (unlikely but it is a possibility),frankly if it was me I would upgrade right now (back up first of course).  Rinse and repeat...

(Thanks for swift response!)
 
--Only happens with 8.53 imports.
 
As far as copying and pasting "the channel" (all the clips?) into a new project, I'm not really sure how that would help anything.  But I'll think about it.
 
I doubt X3D will fix it since this has been going on since all the X2 versions ... but I will upgrade to X3D ... hahahahah!
 
Some work-arounds require stoic discipline and unlaziness: like:
1) Disabling the HP filter for every track and using the prochannel bell EQ instead.
2) Enveloping the HP filter (for every track) (a real treat!) ... if only I could assign a key macro for that!
3) Saving projects ... only when the HP filters are 'behaving'  :):):):)
4) Not allowing Sonitus EQ conversions thru prochannel EQ
5) Or worst case ... disabling prochannel EQ altogether (not likely)
 
Thanks again for your kind thoughts!

> As far as copying and pasting "the channel" (all the clips?) into a new project, I'm not really sure how that would help anything.  But I'll think about it.
 
This has worked on several different occasions as a new Project is X3 native and you are just copying across objects to it, rather than what you have which is a converted 8.x project which has become X3, a process which may not be optimal. It may even help it to convert to X3D.
 
I also recommend the bundle idea as this can act like a washing machine in some instances (Cake recommend this as a sort of "defrag").
 
Just ideas anyway, you never know until you try them.
 

Well I converted from 8.53 --> X2(?) --> X3c already ... and the bug was contagious.  
 
The bug is contagious for ALL the 8.53 conversions I've made so far (about 10 8.53 projects).
 
That still leaves your experiments which I'll try to report on in time ... (1) x3d conversion, (2) cloning across to another project, and (3) bundling-unbundling (which actually seems 'worth a try').
 
Of course I hypothesize that all 3 will fail ... and I'll just have to be blessed with my unlazy work-arounds!
 
Thanks again for your swift and excellent thoughts.

If the other two were not worth a try I wouldn't have suggested them.
Good luck...!