WORKAROUND:
In Windows 7:
Control Panel | All Control Panel Items | Display >> Set custom text size (DPI)
Custom DPI Setting
100%
Check Windows XP style DPI scaling.
See Attachment screenshot: Control Panel Display Set Custom text size screenshot
STATUS:
Issue fixed in version 12.0. The latest version of Toad for Oracle can be downloaded at: https://support.quest.com/download-product-select