possible setback

I've been breeding a bunch of Drosophila melanogaster third chromosomes, from five populations along the East Coast, from one X:2 background into another through a four generation crossing scheme involving balancer chromosomes.  The new background has white+ on the X and they are coming from a white- background.  In the current generation I'm seeing white eyed males when I should not see them.  The simplest explanation, which would not be good, would be if the new background stock (Ral[303]; Ral[303]; TM2/TM6) is contaminated with a white- X chromosome. If this is the case then the stock contains recombinant chromosomes and about a month of work would have to be discarded and restarted.  A less likely possibility would be if the above Ral 303 stock has a high incidence of X nondisjunction in females and the white- males are X:0.  This would not pose a problem to the stock or the lines because these males are sterile.  I'll probably know in the next two weeks as I collect the next generation whose mothers are from the Ral[303] stock.