UPD 2 Mr.Claymore I can repeat this bug now. It happens only with "big" config files and happens only when killing the EthMan.exe process in the Task manager. I also see that EthMan is trying to save the config file, even if it is killed abnormally. And I suppose it just has not enough time to finish the save operation and flush the disk cash.
Why do you kill EthMan from TaskMan? EthMan saves data at exit and it can cause this issue. EthMan cannot detect that you kill it abnormally, TaskMan sends normal WM_CLOSE message firstly, in Win7 it waits then, don't know about Win10.
Why? Because, as I said, I couldn't close it normally. It came to a state, when all miners were red colored as they were not available. And EthMan didn't respond to a "Close" command. It happens earlier or later, but it happens, if EthMan runs for a long time. Can I provide you with any additional helping info? Mmmm, may be... As I said before, I have two EthMan windows opened. Next time I see one of them hangs, I will check if this one gets config wrecked, not the second one, that runs normally.
P.S.But you have at least 2 options:
1) Wait 0.5sec before writing the config at exit
2) Perform a crash safe writing. So, write the temp file first, then make a copy of the current file as "*.old" and finally rename the temp file to a normal name.