CPU cores saturated by OMP code (with 2017 Update 3)

We find that some CPU cores running OMP code are saturated ever since we migrated to Studio 2017 Update 3. The code involving

kmp_set_blocktime(0), "omp parallel sections", "omp parallel for"

 was running fine with Studio 2016.

With 2017, calling

kmp_set_library_throughput(); kmp_set_blocktime(0) 

does not avoid the saturation. However calling 

kmp_set_defaults("KMP_BLOCKTIME=0")

 or 

kmp_set_defaults("OMP_WAIT_POLICY=PASSIVE")

 avoids it. 

Can anyone explain what is going wrong? Is this a bug in 2017?