Well, I am using Creo 2.0 M120 and this is where I see this "weird" behaviour.
I'm curious about your "quick test" in creo 2.0 which says it doesn't happen.
Can you do it again and note the following:
- tolerance mode for the dimension has to be "Nominal"
- you are changing the value of the dimension by double-clicking on the dimension in the drawing or model (so that the little entry box shows up).
I find that under these circumstances, the system will change the dimension's tolerances to match the linear_tol settings (according to the number of decimal places specified for the dimension). The "rounded dimension value" setting doesn't matter. If the dimension's tolerances are set to other modes (Plus-Minus, +/- symmetric, ..) then they will not be changed when the dimension's number of decimal places or its value are changed.