Unfortunately, I can't! When I run the ,ly file exactly as you send it, I don't get the same problem with the red line: it's centered between LeftEdge and BarLine. I get the same result in 2.14.2 and 2.15.8. I can't duplicate the problem you're seeing no matter how I comment the file.
The fact that the red line appears below the note means it hasn't been moved at all (there would have been an error instead in the first version of the function). The function thinks that either (a) one or both of the grobs you want to use to center the red line aren't there (in this case, LeftEdge and BarLine); or (b) they don't appear in a left-to-right order. I can't see how either of these situations would apply here -- no matter what you comment in or out.
I've attached a file with an addition for testing which will display a message on the console if the function rejects any of the input. It will tell you if both grobs are present in the system, and if so, which one isn't suitable to use for alignment.