Wacom pressure sensitivity problem

I got a wacom volito 2 for christmas (probably the cheapest wacom there is)
and it’s served me well for the past few months. Prior to getting this, i had another graphics tablet (even cheaper) and for some reason, after about ten strokes of the pen, the pressure sesitivity would just stop working for one stroke and id end up with a big fat line.

Now i have thrown that tablet away, it was really annoying, but now my wacom is doing a similar thing. In flash i can draw ten, maybe fifteen strokes before it jumps a little and makes a huge fat line.

Is this a problem with my computer or am i just really unlucky in buying tablets?