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If that were the case, I would expect to see efflouresence appear also with paver patios that were not sealed. Since we started using polymeric sand on every single paver project we install, and haven't seen an increase in efflouresence problems (and have never seen it appear shortly after applying the sand), I have to think that the poly sand had little or nothing to do with the efflouresence, whether it was "set" or not. Something for reference - polymeric sand, whether it's the type that uses an organic or non-organic binder, softens a little and resets each time it gets wet (moreso with the organic binder variety) - so that sand is never really completely set.
So I do not think it's the poly sand.
From what you've said, the more likely explanation is that with heavier shade, water stayed in the pavers and base on the affected patio longer, allowing efflouresence to rise to the top. Because one patio has eff. significantly more than the other, I'm inclined to think it's the materials beneath that patio (crushed stone, etc) that have the minerals in them.
I should say again, from what I've read so far, I don't think this is something to be angry at your contractor for. By waiting 1 year, they were doing their best to eliminate the chance of efflouresence coming out of the pavers. And while the crushed stone or bedding sand they used may have been the source of the excess minerals, it would be hard for them to know about it unless they did a chemical analysis on the crushed stone they were buying from local quarries - something that I think should not be an expectation of a contractor. If they use crushed stone from one supplier and consistently have eff. issues, then they should consider re-sourcing their stone.
While it has to be maddening to feel helpless about having this patio with these belmishes and being able to do little about it, I think the best course of action is to do nothing, letting the sealer wear off in it's course, and allow the efflouresence to come out afterward.
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