1. In Writer choose File / Export as PDF...
2. Click "Export"
3. As filename type in "test"
4. Click "Save"

Now a File test.pdf has been created.

Expected Behaviour:
In Gnome and Mate under Places / "Recent Documents" an entry with "test.pdf" is created.

Actual Behaviour:
In Gnome and Mate under Places / "Recent Documents" an entry with "test" is created.

Additional Info: The recently used files are stored in .local/share/recently-used.xbel

So it seems the bug is, that Writer stores the typed in basename under recently used instead of the actual filename that is created.

When typing in "test.pdf" instead as "test" as filename, the correct entry "test.pdf" is stored in recently used files.