Typed characters aren't always visible in edit controls

If a multi-line edit control window is scrolled to the right (for example, in Notepad) and caret is not at farthest to the right position, newly typed characters are invisible. String edited this way updates again only when window is scrolled to the left again.
This happens while typing code into Winamp AVS interpreter. Its code windows are small so writing code can become confusing.
Steps to reproduce: in Notepad, type text string longer that window size. Then move caret away from the right edge and type a character.
Or, type a second string below the first, it will be invisible from the moment the window starts scrolling until caret gets farther than end of first string.
VBox 5.0.20, bootcd-r71673(rosbe).iso