It isn't a big deal if you've been flying both of the jets for a while. Some issues arose with our DECs who didn't have any time on the airplanes and brand new FOs who didn't have much experience were paired together on reserve and they could potentially fly the 2/7/9 in one day... However those days are pretty much gone because our airframes are more segregated by base (not totally but much more than they used to be) and we don't really have a lot of inexperienced crew being paired together like we did during our rapid growth period.