When files are exported or saved without explicitly typing the whole name (with extension) then krita adds an extra period (".") in the file name. 

Simply put, Krita will save a file as "Filename..xyz" instead of "filename.xyz" if you skip typing in the extension in the save/export dialog. Typing the whole name like "filename.xyz" works around this behaviour. This happens irrespective of file type, and in both Saving and Exporting files.

Reproducible: Always

Steps to Reproduce:
1. Open any krita document or create new.
2. Save/export the document, without typing in an extension in the save/export dialog.
3. Observe file name.

Actual Results:  
An extra period (".")  is added to the filename ("Filename..xyz")

Expected Results:  
Filename should be saved in its proper format ("Filename.xyz")

Texted and confirmed on Linux Mint 18 Cinnamon 64 Bit and Windows 8.1 Pro 64bit, both running Krita 3.0