Once the kernel driver (usb descriptor) is fixed then the evdev.conf in xorg.conf.d tablet snippet recognizes the tablet as a tablet. And it automatically sets the tablet to Absolute mode, which is what you want, not Relative Mode like a mouse. Or the same thing happens if you use the WizardPen driver and it works for your tablet.
My guess is when you do the hotplug the device order gets changed and that's why Gimp picks up the pen. If you look at the output from xinput list:
you see the "device name" for both devices is the same. One is actually the pen and the other can be the mouse or frame buttons on the tablet. Some of the app.s like Gimp are set up to handle Wacom and the Wacom X driver appends the device type (stylus, eraser, cursor/mouse, touch) to the "device name". That way you know what to set to screen in Gimp. Fortunately usually the first UC-LOGIC device is the pen, but not always as you have found.
⎜ ↳ UC-LOGIC Tablet WP8060U id=12 [slave pointer (2)]
⎜ ↳ UC-LOGIC Tablet WP8060U id=13 [slave pointer (2)]
You can figure out which is which by running:
Where you get the ID# from xinput list. But as you see order apparently can change.
xinput list-props ID#
So anyway there is a problem with the current setup. Either the app.s have to become sensitive to the flag the kernel is putting on the device type or the device type needs to be appended to the device name. We've been talking about this issue for quite a while without a solution. Not sure how likely it is the evdev maintainers would accept code to label the device type like the wacom driver has. But a few weeks ago I found a submission to the kernel's input mailing list where a dev. submitted a patch to append pen to the device name for a touch device that could also use a pen. Nick wasn't real thrilled with using similar code for UC-LOGIC because he would like a more general solution. But it looks relatively simple to me.
Easy for me to say because I wouldn't have to code or submit it. So if the kernel's input maintainers accept the other guy's patch and Nick finds some time to code and submit it we might finally have a solution.
I suspect this limitation is one reason the WizardPen driver only worked for the tablet pen and never the tablet mouse. It blocked the mouse input.
In the meantime we may be able to set up a custom .conf to block any tablet device but the pen. Do you have a tablet mouse or is the other device tablet frame buttons?