Unnecessary and incorrect thumb rebuild CS5 BR5

Question

I installed Xrite's colorchecker passport system and created a DNG test profile.  I created exactly one image in a test directory and applied the generated profile to that image.  This was successful.
Subsequently, I opened two other directories with about 600 CR2 raw images each to select images for editing. Various images were previously "generally" adjusted in ACR.   After the test of the DNG profile, in both cases, Bridge chose to rebuild thumbnails and assigned a colour temperature of 12500K with a -0.35 exposure adjustement  (which are similar to the values determined in the DGN profile test) to almost all images and recorded the information in the xmp files.  Those CR2 raw images not adjusted were those that I had edited in ACR extensively and used PS5 and had an associated PSD file.
When does Bridge choose to rebuild thumbs?  Seems to me that, once the master and directory cache is generated, the only time the thumbs should be regenerated is when a raw file is modified in ACR (via the xmp file) or when a PSD or JPG is edited.  Changing any attribute in ACR should not cause general thumb rebuilds - it should only effect the single edited file(s).
I am reluctant to look at other directories for fear of the same situation recurring.
tony

Answer 1

further note:  in directory C:\Documents and Settings\tony\Application Data\Adobe\CameraRaw\Defaults, there is a file Default_140c2e...xmp that contains the erroneous WB information and is date stamped with the curent date+time - about the time I was playing with the DGN camera profile.  In addition, there is a "previous.xmp" file also stamped with a time but contains IMHO valid information.  I moved the "Default...xmp" file out of the directory.  Subsequent opening of directories with Bridge no longer builds thumbs unexpectedly. 
Looking through ACR, I cannot fine a way to "savet defaults" (but I may have missed it).   This default seems to be magically generated - but I don't know under what conditions.
Does ACR changes (and updates) cause Bridge cache to be re-processed????