Editing an imagefield widget inserts default file_extension text back in

We created an image field.
Removed all file extensions from the acceptable list.
Saved the image field.

Creating a node shows no file extension restrictions in the field description text. Great.

Re-editing the widget settings the code checks for the $widget['file_extensions'], and if empty inserts the field with the default 'jpg jpeg png gif'.

Should it really be doing this though? Its effectively overwriting your settings if you go to change anything else in the widget!

The offending line:
456: '#default_value' => $widget['file_extensions'] ? $widget['file_extensions'] : 'jpg jpeg png gif',