Path autocompletion doesn't work when the line is longer than MAX_PATH characters. To reproduce, paste the following into a document:
Place the caret after the "p", and press Ctrl-Alt-Shift. Nothing happens. It should bring up autocompletion (probably for c:\progam files, but it depends on the c: drive of course).
If also think path autocompletion should work if the drive name is preceded by parenthesis.