I cant tell you how many times I have read that one should not heat sugar syrup after adding the sugar. I have seen various reasons such as preventing carmalization, production of HMF, etc.
Now one can search this forum and find numerous posts about making hard candy, fondant, feeding hard candy, and its usefulness in supplemental feeding during cold months, or frankly during the summer as well.
When one makes hard candy, you heat concentrated sugar syrup to very high boiling temperatures (much higher than you would get with 1:1) near 250 F to drive off water and essentially make hydrated molten sugar. Now if this isn't high enough to make toxic by-products then certainly boiling dilute sugar syrup is not going to do this. I haven't seen anyone complaining that the candy killed their bees.
As you can see this is a great inconsistancy of advice with respect to boiling syrup, which does greatly increase its longevity for storage (ie kills fermenting yeasts and bacteria). So why is there this discrepancy in advice?