Can’t add custom file extensions

I am currently using [multilinefile attach sh|bat] to allow sh and bat files to be uploaded to one of our forms. This doesn’t work. The first time I submit it gives the error “One or more fields have an error. Please check and try again.” and no further feedback. If I try to attach the file again I get “You are not allowed to upload files of this type.”.

It looks like the sh|bat text that I am passing in via the contact form is being lost in mfcf7_zl_multilinefile_validation_filter() and it falls back on “Default file-type restriction”. I am unable to find a way to override this without modifying the plugin code to use sh|bat in the default text, which is not ideal but my only option at this stage.

Any help appreciated.