Thanks Martin, yes i am familiar with how the package temp is calculated but to be clear, this scenario is reproducible over and over just by toggling the setting.
i have of course switched to bus clock-based enabled.
Strange issue since it does not seem there should be any connection between this setting and the sensor core temps, however when i turn off the option for Bus Clock-based CPU clock measurement, my reported Core temps are 4-6 degrees lower (at maximum load) than the CPU package temp and other cpu...