When the filesystem is vFAT, upper and lower case extensions are found. With NFS, the filter *jpg does not find files ending is .JPG and all of the variations like .JPg, JpG, etc. My camera producing files in the form P*.JPG.
Since it really is file type defined by an extension, I think mixed case should be allowed for a *.jpg filter. You can't practically add all of the variations case for 24 file types and probably regular expressions are not allowed as filters.
workaround - any file that can be uploaded has to have a lower case extension.
A full discussion is here: http://www.electro-tech-online.com/threads/uploading-images-case-sensitivity.146854/#post-1246240
Upload file filter
Case sensitive file systems
Linux 12.04 LTS