This is unexpected as I have a different story (opposite as to what you were having).
I had an issue with this with my TP (3.0.2) with the P and backspace not responding properly (specially if you tap it consistently).
I already called HP to the point that they sent me a replacement for this device. The replacement was actually worse! The m, p, i, q, backspace, number 8 were not responding to my touches.
At one point, I had two TPs at hand and I was thinking that if I'll just keep my older one (the one that was supposed to be replaced) or the replacement TP.
Fortunately, 3.0.4 showed up and I just updated both.
To my surprise, both touch issues were gone after the update. It magically disappeared. Also, protective skins like skinomi (clear) had bad effect on my touch as well but probably that isn't your case since you were fine before the update.
The method I used for update is, erase USB first > then secure full erase > the doctor. This is not advisable but maybe you want to try it.
EDIT: I forgot to mention that all positions (portrait/landscape) had the touch issues on mine. So I believe it was funky software - that is one of the reasons why I was puzzled on HP supports decision on replacing my TP.