Well, apparently it happens if you try to re-acquire an already acquired device, like keyboard, mouse or joystick/wheel. I guess you try to re-acquire as soon as LFS gets focus, but it seems like losing focus does not always actually lose the device handle, so when focus is regained there is a chance the DIERR_HANDLEEXISTS pops up. From what I've read that's simply an info message and doesn't actually do any harm, so a way to "fix" this "error" would be to simply not display it anymore.
I guess you could also try to poll the device to see if the handle is still there, and only if that fails try to re-acquire it. That should get rid of the message, too, but I don't know which solution is the better one. The former one is definitely the faster and an IMO not too horrid one, so I'd go with that.
I guess you could also try to poll the device to see if the handle is still there, and only if that fails try to re-acquire it. That should get rid of the message, too, but I don't know which solution is the better one. The former one is definitely the faster and an IMO not too horrid one, so I'd go with that.