Wrong task or conditions

I would like to give some feedback about ...

From: https://py.checkio.org/mission/sort-by-extension/solve/

HTTP_USER_AGENT:

Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/87.0.4280.88 YaBrowser/20.12.1.179 Yowser/2.5 Safari/537.36

The files with the same extension should be sorted by name. But why assert sortbyext(['1.cad', '1.bat', '1.aa', '.bat']) == ['.bat', '1.aa', '1.bat', '1.cad'] '.bat' goes before '1.aa'. It should be sorted with '1.bat'?