What is driving the MB of a stack?

[dfepstein at comcast.net]

Thanks to Scott Rossi and Richard Gaskin for their suggestions, which led me to the problem (large block of data stored as a custom property of a substack). 

  

While poking around, I noticed that many but not most controls and groups, when I get "the customPropertySets" of them, return the value "cREVGeneral", although when I look for this in the property inspector I do not find it.  What causes this custom property set to be created for some but not all controls, and (assuming it is really there), is there any harm in removing it? 

  

David Epstein