Text in the Editor is being highlighted when moving the cursor with the arrow keys.
After typing in a script in the editor, e.g: select * from TABLE_NAME; if you then use the arrow keys to move the cursor to the start of the script, the text that has been written into the editor is highlighted automatically. It is the same behaviour as if the Shift key was constantly pressed in when moving the cursor around the text.
This is due to a setting in Toad options.
Go to: View | Toad Options | Editor | Display | then Untick 'Persist Selection When Using Navigation Keys'.
This will turn off the text highlighting when moving the cursor with the arrow keys.
If the above option is already unchecked then there may be a corrupted toad.ini
1. Close Toad
2. Rename toad.ini located in <Toad installation folder>\User Files
3. Relaunch Toad