A functional change was made 7.1i MAP to automatically apply a "KEEP" constraint on nets with Directed Routing constraints, to prevent them from being merged into logic. MAP was also incorrectly changed to also apply an "S" property to these nets, which prevents them from being trimmed when needed. The result is that a design might have loadless or driverless nets, which will lead to a DRC error during BitGen.
This problem has been fixed in the latest 7.1i Service Pack available at:
The first service pack containing the fix is 7.1i Service Pack 2.