Fingers crossed for the pull request.
Is there a workaround in the meantime?
I am also experiencing this 1.37.1 - Using GTK+ v2.24.32 and GLib v2.66.2 runtime libraries on Windows 10 64bit
a file `foo.markdown` is indeed detected as filetype markdown, but the markdown preview tab shows that same
The current document does not have a Markdown filetype.