The NET PERIOD constraints are been pushed from the REFCLK input to the RXRECCLK output of the GTP/GTX components. RXRECCLK is a recovered clock, generated by the data transitions in the GT. Only in some configurations the input clock is related to RXRECCLK, but the majority of the time the constraint system should not push the NET PERIOD constraint from the REFCLK input to the RXRECCLK output.
When is this going to be fixed?
This is a known issue. This is scheduled to be fixed in 11.3.