Miner sometimes misreports hashrate

[gertjaap]

See #64

It seems more likely that the software is misinterpreting the hashrate from the underlying miner output. What would be helpful is to enable debug logging (this adds additional log overhead, but at least we can catch what the miner's console output is during this event). Then when it occurs again, upload the debug.log to this github issue, then I can fix it.

[gertjaap]

I've had no reports about this since this issue was reported, and no debug.log while it happened. If anyone manages to catch this problem in the wild and recorded a debug.log of it, please post it here and reopen the issue.