VERY MYSTERIOUS !

Six weeks ago we had three new d/g UPVC windows fitted, Argon filled, K glass all the bells and whistles...a brilliant job! Not a problem of any sort, until today! Pulled back the curtains to find a 3 inch band of condensation along the bottom of the largest pane..the other two windows with no sign of it. My immediate thought was the seal had gone, only to find a complete mystery, in the fact it was on the OUTSIDE...never experienced that ever before...so hot footing over to see the suppliers this morning, to ask what's going on, C/W photo of course:)