The wordDefinition property in VSC includes the "." and "" characters as word separators. This makes the completion suggestions complete incorrectly.

For example, since any suggestion with "" or "." is not a word the following problems will happen:
Type 'notepa' and choose 'notepad.exe' and it will complete as 'notepad.exe'. However if you type 'notepad.e' and choose 'notepad.exe' and it will complete as 'notepad.notepad.exe'.

Or

Type 'C:' and there will be a list of paths to choose from, but if you keep typing '_C:_' the examples go away. If you still continue to type a real path like 'C:\Use' the suggestion 'C:\Users' will come up but if you choose it will complete as C:\C:\Users.