This may be related to bug
Enter some text into the CodePad, but don't press Enter yet.
Highlight the text using the mouse. Highlight the entire line and go as far left as you can; this will take you a few pixels beyond the left margin of the text.
Press Delete (not Backspace) to delete the text.
Type some new text, such as a variable declaration (eg: boolean x). Press Enter.
BlueJ will return an error because it lost the first character of the new text.