This is probably rather a glitch than a bug, but it does give a bit of an unpleasant look-and-feel:
Currently, with folders like "best of 90s vol.2", extension column will show as '2' because the dot is recognized and everything beyond the dot is regarded as "file extension".
However, that's a container of files, i.e. a folder, not a single file.
This is what happens in v1.2.0. Lubuntu Trusty.