Digestion of pRSETA vector leads to funny migration profile - (Jun/12/2013 )

I am running agarose gels of Eco RI digested pRSET A but the cut vector shows lower mobility than the uncut
Is this a problem specfic for pRSET ?

coiled DNA (uncut) runs faster than linear DNA.

Yes I am aware of that-but I am not able to figure this one out-the cut band shows the expected soze of 2.9 kb but i wonder if it is Star activity of EcoRI or something else -like nuclease contamination somwhere-now trying out with other cutters of pRSET