I have to admit, I haven't used that part of the tracer in a long time. Typically, when I want to know where in my trace a property has been changed, I use the binary search idea. For example, if my trace is 10,000 lines long, I look at line 5000 and if my property is not yet changed to the interesting value, but it is changed to the interesting value by line 10,000 then I look halfway in between at around line 7500 . In that manner, I quickly zero in on exactly which line is of interest without using the property-change feature.
However, if you are finding that the property-change feature is not working as documented, or that the documentation is inadequate, I suggest you file an SR since that is a defect we'd like to address. /Eric