Why is a node with the synthesis attribute keep not preserved as intended?

Description

Due to a problem in the Quartus® II software version 11.1 SP2 and earlier, a node with the sythesis attribute keep may not be preserved as intended when the Rapid Recompile feature is turned on for the project.

Resolution

To work around this issue, turn off the Rapid Recompile feature.

This problem is fixed beginning with the Quartus II software version 12.0.