Dan Winterland - Spot on, the phenomenon is just as explained. The aircraft may have a 'span' of 70m but with a swept wing i.e. 747-400 the actual wing length may be, say 72m. Hence when the aircraft turns to access it's stand spot the wing appears to grow catching out the unwary!
Hammered into us in basic trade training in the RAF many years ago, the examples we were quoted were most commonly the VC-10.