I am filling by way of a spigot, leaning the bottles at an angle and carefully running the beer down the side of the bottle, as to not agitate it.
The One Step, from my understanding works by releasing oxygen during its sanitizing process.
So when using One Step to sanitize the fermentation equipment should not be a problem because oxygen introduced to the wort is a good thing.
However when using the One Step to sanitize the bottles could be the problem. The residual One Step, left in the bottles after sanitizing, maybe introducing oxygen to the beer after fermentation which could be leading to the bad taste.
Just a theory I am running with, hence the reason for the rinse after sanitizing. Adding distilled water to each bottle, for the rinse, from a sealed gallon jug, seems fairly low risk for contamination.
The use of corn sugar was really the only other thing I could change to the bottling process, which could, maybe, effect the taste.