In my design, the configuration of the RAMB is block RAM and FIFO in ECC configuration with PIPELINE and Block RAM in Write First or No Change mode.
However, the value used for pulse width check is 1.887ns (530MHz) instead of 1.515ns (660MHz).
As per the datasheet, (DS893)
Pg27, "Table 27: Block RAM and FIFO Switching Characteristics"
FMAX_ECC for speed grade -3 in this type of RAMB configuration is 660MHz.
This is a known issue.
The FMAX_ECC value in this configuration should be 660MHz as documented in datasheet.
The issue will be fixed in the 2015.1 release.