Some brand new sliding patio doors (usually solid wood core) have been found to leak air where the operating door interlocks with the stationary panel.
This often does not become apparent to the owner until cold weather sets in.
The reason cold air is felt blowing in around this interlock area is because the doors are not fully interlocked and the weather seal is not fully engaged. This can occur even if the operating door is fully closed and securely locked.
The cause is due to the fact that the patio door system is likely about 1/4" too wide for the opening, the door was installed to be plumb and not square (and a 1/4" was lost)... or, the manufacturer made one or more of the components a little too wide and the installer did not have enough of a financial cushion in the job to take the time to correct the error. http://www.dehavenconstruction.com/vinyl-window/window-installation-errors-problems.php
The solution is to remove the stationary panel, plane the vertical jamb side and replace.