Other file browser extensions "not allowed"

Hi there. Under File Browser > "Allowed upload file extensions," I've added other file extensions such as pdf, doc, docx, xls and xlsx; but after saving these settings, the image browser still refuses them. I've updated the db and cleared cache in case this was an issue, but when inserting an image and browsing to upload/hitting "send," receive the message "filename.pdf not allowed."

Granted, I realize that these are not actual web image file types. The intent is to use the browse/upload feature as a back door for authenticated editors to upload supporting files. My users would not actually be continuing on to insert the images with the tag into the html.

This is the workaround I've been using in IMCE, which is a less intuitive interface than Whizzywig's Image Browser. My clients all have supporting .pdf files or other working documents they need to be able to upload and link to, and image browser seems to be the best solution I've found so far to easily accomplish this.

I'm actually using Whizzywig 6.x-2.2, which isn't listed in the current version pulldown menu for support requests. (Using whizzywig61.js as the most recent released library file).

Many thanks for any info as to why other extensions aren't being accepted in the file upload despite setting access for them in the extensions field?