image upload to custom field breaks if resource url not default

go to directories and resource url settings and change the image folder location for each to /images (instead of persist/contribute)
create a file-type custom field on the contact record
upload an image to that field

the image thumbnail now appears. but when you click the image to view the large version, it breaks.

the issue is:
CRM/Core/BAO/CustomGroup.php
line 600

when we build the imageURL value, we retrieve the imageUploadURL (configured above) and do a str_replace so that it retrieves the file from the custom folder – not the images folder. that's because ALL file type custom fields are stored in the custom folder, but we're borrowing the url construction from the imageUploadURL to create our hyperlink.

the problem is that by hardcoding the str_replace values, we don't account for anything but the default setup. by changing the locations above, we break the url construction.

i'm not sure the preferred way to fix this.