iOs 5 first gen iPad.
iOs 6 third gen iPad.
Both will on occasion lose the right margin such that it cuts off the last half of a letter on a line.
It seems unpredictable though I alternate between Mantis and Note Taker HD when I study.
Might Note Taker HD may be leaving something behind in a register?
Typically a power off of the tablet will fix the issue but recently had the third gen iPad refuse to fix the problem with a power off. I had to delete and reinstall Mantis to fix the problem.
Have never seen the problem on the iPhone 4s