This problem affects DDR2, DDR3, and LPDDR2 products.
The Cyclone V pin-out file identifies some general I/O pins that you should connect to ground when using the hard memory interface on Cyclone V devices. If you do not ground these pins, your design might experience increased crosstalk from neighboring I/Os, or reduced maximum frequency capability.
There is no workaround for this issue.
This issue will not be fixed.