Does sounds more like a software problem with IE or a page you are viewing is doing something in the background, or you have other processes taking priority.
Well, that was my first though too, because in fact I have first experienced the issue in my own software.
However, further investigation revealed that the same problem is visible in all applications. And task manager shows zero cpu usage.
Furthermore, another indication was that when I slowly move the cursor over the edit field, it "jumps" a bit right down and then back. That indicates that cursor hotspot is in fact correctly changed (I-beam has different hotspot), but the new cursor shape image is not displayed.