Mint 18.3 sending monitor to sleep with KVM switch

[tuzzer]

Hello,
I don't know if this is the right section to write in. I'm not sure if this is more a hardware or software issue.

Situation:
Mint 18.3 xfce on an old Acer eeeBox nettop pc
Monitor, keyboard and mouse shared with a Windows7 pc

The Acer is working fine, the only issue is that when I switch to the PC and then back to Mint, the monitor goes in suspend mode because no signal is detected. This only happens if the user was logged in Mint when the switch was done.
Otherwise, if the user logs out first, and the switch is done when the welcome screen is on the monitor, switching back to Linux goes fine and the log in goes fine.
When switching to Linux and monitor suspends, tried to power-button-suspend the Acer and then power-button-wake: the gtreeter appears, but after inserting username and password i only get a black screen.

I have tried various combinations of power management: no timed sleep, no screensaver, no timed screen lock and so on and then no screen management, then back on screen management, presentation mode on and off, and so on.
No resolution switching problem, both the pc's have 1366x768 (or something similar, anyway, the same on both, and refresh rate too)
I started to think that if it was a hardware matter, the same suspend issue should happen even without logging.
Is it something that can be solved disabling or adding some power management related service? Something which is (or is not) running while the greeting screen is on?

Thank You

PS
same thing happens with Mint 19 xfce