UPDATE 8/3/2015: The system exhibited similar (though far less pronounced) symptoms without the KVM being plugged in, so it may have been the mouse starting to fail that caused the dropped connections. I've tried a new mouse and it seems okay, but still need to set everything back up again with the KVM to clear its name.
While it looks like I was too hasty on the judgement, the frustrations with the device still stand. Post title updated to reflect the discovery.
A little over 12 months ago I bought a PCT-MP4711 4-port DVI/USB KVM to switch keyboard/mouse/monitor between two or more machines.
In the last week I started noticing some drop outs where the mouse/keyboard
would lose "sync" for a few seconds. While working this is annoying,
while gaming it's catastrophic. By coincidence I'd just installed a new
router at the same time, so I initially thought it was a network issue,
have now proven it was the KVM.See above: perhaps not
I noted at the time that the 1 year warranty was a bit worrying, and it turns out I was right to be worried. It lasted essentially the 12 months and a few days before becoming unusable. You get what you pay for, etc, etc.
The thing always was a bit temperamental — particularly the key-based shortcuts to switch between settings. Sometimes you'd have to press the combo three, four, five times or more to get it to register. And sometimes it would stop working and require the USB connectors (which give the box its power) to be disconnected to reset the thing.
In the end it was an okay experiment, but I don't recommend anyone buy PCT equipment based on my experience. Unfortunately other equivalent options are much much more expensive, so while it was an okay stop-gap, the lack of longevity is a major let down.