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Concrete topping over wood joists

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I have a problem from a job that I designed about a year ago.  The topping of 1.5" lightweight concrete specified by the architect has come unstuck in some places.
It seems to be near support lines that the problem occurs, which means that it is probably because of deflections in the underlying joists on each side of the support line.  (Like cracking on a steel deck and concrete floor over girder lines).
It is not just cracking of the topping along the support lines, however.   It seems to have cracked about a metre to the side of the support line, creating a cantileverd portion of the topping still attached to the topping on the other side of the support line.  (This would be easier to describe with a sketch...)  The cantilevered portion moves when you walk across it.  The client's not impressed.
I specified these joists to have L/360 deflectin limits under live load, L/240 under total load, and I am sure that this has been respected. 
It would have been nice to have specified some sort of saw-cut or tooled joint above the support lines.
How is this treated normally?  Has anyone had a similar problem?  Any comments would be appreciated - much appreciated.
Kevin Below
Génécor inc., experts-conseils