interesting coin flip problem

[PaultheS]

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All coin flips are completely independent. Regardless of how many you intend to flip and and how many you have flipped already and there results, each coin flip will have a 1/2 chance of being heads or tails. This deals with the law of large numbers. We can't apply the law of large numbers to a scenario in which there are only 2 trials. The greater the amount of trials preformed, the lower and lower the standard deviation becomes. When tossing coins, no matter what, chances are 50-50.
Knowing that you're tossing two coins does not change that.

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Yes, all coin flips are completely independent, but flipping two coins in a row is not the situation that is being dealt with here.

The question is: I flip two coins. Given that at least one landed heads, what is the probability that one coin was tails?

This is a very different question and has nothing to do with the independence of repeated coin flipping trials.