When crossing SLR, derates (slow down or larger delays) or prorates (speed up or smaller delays) are used to emulate the effect of mismatched die.
What should happen is that the uncommon delay is prorated 15% in slow analysis and derated 15% in fast analysis.
What happens due to a bug is that uncommon delay is always prorated 95%.
This can result in under-reports or over-reports.
When the destination clock delay is affected (generally setup) it could be by around 1ns.
When source clock delay and data are affected (generally hold) it could be by several nanoseconds.