This is a somewhat common problem. Your application has an overlay <div> element at the top of the browser window. Test Studio, when you have SimulateRealTyping, selected always wants to scroll the element to the top of the browser window in order to make sure it's visible in the browsers window before trying to type into the input box. Unfortunately in your case this has the side effect of scrolling it underneath your overlay div.
The only way to over come this is to convert the step to code then comment out the ScrollToVisible line of code, like this:
// Enter text 'passUser' in 'UsernameText'
, 50, 100,
The side effect is now you have to take extra care to insure the input box is visible before that step runs. Else typing won't go into that input field.
I hope this helps.