In the liberty file, it is define the timing arc, in a table. The parameters of this tables are the transition and the capacitance.
When a net violate a max cap, the tool extrapolate the timing, because it can't find the value in the table inside the lib. The formula uses for the extrapolation could not reflect the reality, and if the violation are very huge, the error on the timing could be very high.
So you need to check all your trans & cap violations, to see if this violations occur on important signals and if the violations are hugh or not.
In general the PR tool correctly fixe the cap&trans violations, but some time you need to fix by ECO steps.