Repeat bars not working on 2nd time through

I have a 2 measure repeat which plays normally (i.e. repeats Ok on the first time play through, but when the the piece goes back to the "Sign" (Dal Segne al coda) the same 2 bars do not repeat but play through only once. I've tried deleting and reverting the offending bars but the same behaviour exists. Is this a bug ? I assume that I've set the repeats up correctly as they work fine on the first play through, and only fail to repeat on the "Dal Segne"

Les