Problems with producing these or underestimate demand?
If they had problems producing these, I wouldn't think it would have any affect on the supply schedule for the new quad core part. Given AMD's current ability to produce quad core parts, it is very likely that defective Hexacore parts would have at least four functional cores and could then be sold as quad core.
However, if they underestimated demand, reallocating resources to produce more hexacore parts could cause a delay in the release of quad core parts. This seems to be the more likely scenario.
... I'm wondering whether AMD will increase prices.
Unlike with the HD5850, AMD's hexacore processors aren't in the position of be clearly superior to the competition while being priced less than the competition (~$350 for GTX285 vs ~$260 MSRP for HD5850 before price increase). Keep in mind that AMD did not raise the MSRP for the HD5870 (still at ~$380), board manufactures raise those prices themselves. That said, I believe it is more likely that AMD will leave the MSRP for their hexacore processors alone. However, if demand is outstripping supply enough that AMD can raise the MSRP and still have shortages for the foreseeable future (unlikely), then they could and should do so.