no file extension added when using 'Save As'

When I use 'Save As' musescore will provide a suggested file name including extension (.mscz) and the full fiile name will be highllighted/selected. So when I type in a filename of my choice the full name including extension will be overwritten.
When I now hit Enter I will get error "Cannot determine filetype". Apparently now the extension is not added automatically but I have to type in the new filename including the extension manually.
Using commit b2e10c7 on Archlinux