The "Content Type" option in FKM is commonly unset as in the below screenshot. This defaults to text file format.
The Content Type can be can be set to "Unicode Autodetect" if the file in question is UTF-8 or UTF-16 format. At present if this option is chosen and you require to use the FKM Default Ignore File name option as in the below screenshot the ignore will not work.
There is a current bug report COL-5759 outstanding to address this.