Okay so there have been many reports of the ways in which the Milestone screen can act oddly... but here is one I just managed to crack.

With the phone sitting on an insulating surface, running Multitouch Vis Test, and plugged into the charger, I press one finger down on the screen. The spot under my finger wiggles around a lot - e.g. x1 goes from 86-94 and back, y1 goes from 590-610 and back. Now, with my other hand I touch the phone's casing... and the wiggling stops, locking into one coordinate.

Now, pull the plug out... anomaly goes away. It only happens when my finger's on the phone.

Why'd I notice this? Because in Swype, to obtain certain alternate letters you have to hold your finger down on a button. But the anomaly makes Swype think I'm wiggling my finger around and trying to Swype a word. So I hold down K to get a semicolon and instead it types "Jj" or "mk" or "ooo".