sometimes the nib in the pen will get a catch on it, and it refuses to "unclick" when you let up. i've had this happen mostly on my older wacoms.
what i usually do is take the nib out with some tweezers and gently file down the edges of the inside tip, then re-insert it. i'm not 100% sure that's your problem, but i've had to do it a handful of times over the years of using wacom tabs.
if it is not a physical problem with the pen nib, are you using windows? i find that disabling all of the little windows pen input extras makes using a tablet a lot smoother.
hope that helps