Try the following:
1) Open PLSQL Developer
2) Un-maximize PLSQL Developer
3) Open a blank program window
4) Maximize the program window
5) Type enough text in the program window to cause a horizontal scrollbar to appear
6) Ensure the horizontal scrollbar is scrolled all the way to the right
7) Maximize PLSQL Developer
Now the text will probably all fit without needing a horizontal scrollbar, but the left-hand side of the text is still "scrolled" out of view. A horizontal scrollbar is present, but the slider takes up 100%. You can use the keyboard or the scrollbar's arrows to get all the text back into view and restore sanity.
1) Open PLSQL Developer
2) Un-maximize PLSQL Developer
3) Open a blank program window
4) Maximize the program window
5) Type enough text in the program window to cause a horizontal scrollbar to appear
6) Ensure the horizontal scrollbar is scrolled all the way to the right
7) Maximize PLSQL Developer
Now the text will probably all fit without needing a horizontal scrollbar, but the left-hand side of the text is still "scrolled" out of view. A horizontal scrollbar is present, but the slider takes up 100%. You can use the keyboard or the scrollbar's arrows to get all the text back into view and restore sanity.