The CORE Viewer tool reports a false utilization for a number of cores.
The affected cores are:
8b10b Encoder V3.0
8b10b Decoder V4.0
These are also known as XST cores. CORE Generator runs XST Synthesis to generate these cores; for each core, this also results in the generation of an EDIF netlist and multiple NGC sub-module netlists.
CORE Viewer reports this incorrect information because it is failing to look at NGC files for source utilization.
If you are using any of the cores above, please use the MAP tool, which will report accurate resource utilization.