I noticed this back when Sense ICS leaked out but it was never fixed. Then I moved on to AOSP roms which don't have this problem but I want my 3d back so I'm back to sense roms and the bug is still there even on newer sense roms. Note I haven't tried the Sense 4 roms as they are less functional than AOSP roms.
The cursor moves randomly. This is specially annoying when typing in forums. To recreate this bug it's simple. Just log into any forum and type a comment. Right away you may notice the bug after you type your user name when you click on the password field sometimes your username will flash in the password box momentarily. Now type out a couple of sentences in a comment box. At this point sometimes the cursor repositions itself mid sentence while you are typing. Again this is random so it doesn't always happen but typing fast (with either stock, swype or swiftkey it doesn't matter) seems to make it happen more often. Now if that doesn't make it happen try editing a word in the middle of the sentence not by selecting but by putting the cursor ahead of the word and hitting the backspace arrow. You'll notice the word will get deleted then magically reappear making it near impossible to edit text. Sometimes the entire word reappears and other times only some letters in it reappear.
What can you do about this?
If you are on a sense rom. Can you replicate the bug? What rom are you using? What browser? Do you know of a workaround?