I have exactly the same problem, on dell venue 11 pro. very erratic behaviour, sometimes it works fine, some other times double letters everywhere and impossible to use drag and drop actions, the items are dropping at random. also windows 8 side swap actions working very badly.
I've been discussing the duplicate/multiple character issue with Dell Technical support since I received my Venue Pro 11 in January. My experience is identical to yours. I've just reached the third tier of Dell support and my trail has come to an end. Dell considers the issue resolved as is outlined below. While I was not in a position to send my Venue Pro 11 to Dell for testing and accept a replacement, perhaps others are. I find it concerning that new units that have been recently purchased are also reported to possess the same duplicate/multiple character issue. Dell considers new reports potentially related to screen protectors since they believe that they have previously successfully resolved the multiple character issue with a firmware update. So, if you have a new Venue Pro without screen protector and continue to experience the same problem, you should contact Dell and they will test your unit and provide a replacement. Here is the text from third tier Dell support: "The problem is I found internal documentation that tells me our Engineering has investigated this exact failure and the firmware released resolved the issue for most of our customers. Normally we would offer a new replacement in order to capture yours to replicate the issue here, and then get to engineering. Since this isn’t really an option for us then the truth is there isn’t a whole lot we can do. I wish I could do more. Please let me know if you have other questions or concerns and I will be glad to follow up."
We have 6 of them for business and all six of them do the same thing. Using them for business is very frustrating because we have customers with tons of misssssspellllledddd words. Again I have 6 out of 6 doing this. We are waiting for Dell to give us a solution.
For what it's worth, here are my experiences. I had this issue, it was really annoying. Dell decided it had to be hardware, so they replaced the touch panel & screen. It made no difference whatsoever - clearly it's not faulty hardware, it just bad design (or bad software). After the A09 BIOS things improved dramatically, I also noticed that using the touch panel firmware from the 7130 helped, although I was still suffering to some extent. Then I noticed that people with screen protectors were having more problems than the rest of us, so I tried giving my screen a good clean. That helped quite a lot, but I was still suffering sometimes. Then I realised that I use the tablet in a lab, with rubber gloves on. When I wear rubber gloves, I get loads of repeating characters, when I use it without gloves, it's much better (not perfect, but usable).
So, my conclusion would be:
There is definitely something wrong with the hardware or software design - I can use my phone touchscreen when it's dirty, with gloves on, and it's fine. That's not the case with the venue 11 pro.
There were definitely bigger problems earlier on, but BIOS & touchscreen firmware updates have (for me) almost eliminated them, as long as the screen's clean, and I don't wear gloves.
I have also realised that a bit of grease or dirt on the screen affects the performance considerably. As you say, it should not be, as it does not happen in ANY of my other touch screen devices, including other tablets.
Also, I found out (on my 7130) that it depends a lot on how/where I hold the tablet. For example, if I use it laying down on a table, I get a lot of multiple keystrokes, while if I grab it in my hands, the problem diminishes.