[HECnet] KLH10 not idling host CPU

I'm posting this here in the hopes that there are other KLH10 emulator users on HECnet. I've been using KLH10 with the tap patches for years and years, and idling has always worked fine. At some point over the recent couple of years, idling stopped working for me on linux (I run ubuntu 16.04.4 LTS with latest updates as of yesterday, on a 64-bit intel machine). My CPU is stuck at 100% utilization, without even starting an emulated OS (I run TOPS-20). In fact, as soon as I type "GO" in KLH10 and before doing anything else, the CPU immediately shoots to 100%. Is anyone else seeing this? In older versions of ubuntu/linux this didn't happen. Thanks, Mark