[polyml] Assertion `costMin > userGCRatio' failed

I am getting the following assertion failure with Poly/ML 5.6:

eg_test: heapsizing.cpp:602: bool HeapSizeParameters::getCostAndSize(POLYUNSIGNED&, double&, bool): Assertion `costMin > userGCRatio' failed.

To get some timing stats, I was running a test application repeatedly to take an average time. It would appear that the sooner I re-run the application after the previous run has terminated, the more likely the above failure is to occur. There is no failure when I run the test once per second manually. Running the test application in quick succession using the command ./eg_test ; ./eg_test gives the failure every 3 to 4 invocations. Is there more information I can provide?

Poly/ML 5.5.2 doesn't exhibit this issue.

Phil