Hey Rick, thanks so much for the quick replies! I really appreciate the feedback.
I tried what you said, it seems it doesn't matter if Windows Ink is on or not: Turning Windows Ink on or off is part of the "Set-up your Pen and Touch" control panel. Wacom's driver changelog states that they recently added the option to turn Windows Ink support off which solves a whole host of problems, including the dreaded mini-lag every time you set the pen down. But yeah, they're not related I don't think.
I did some more testing and you're absolutely right, it's isolated to the top left corner.