I have Adobe Flash CS6, and a XP-Pen Artist 12 drawing tablet. Whenever I use pen / tilt sensitivity to draw a line in Flash, the line has a giant blob on the end of it like this:
Is there a setting or something I need to change in order to remove this blob from my lines?
Not in Flash.
You may be able to play with the driver settings switching on and off every single one. Look into all the "Tablet PC Settings" and "Pen and Touch" in Windows Control Panel also. No guarantee, but worth a try. Only Wacom devices are officially supported and CS6 is a version that is many years past its support time.
CS6 is also the best Flash to date.
If you want to use it hassle-free, buy an Intuos Pro.