In 2.4.5.9 "Durations",
in the algorithm for "parse a duration string",
step 8 says:
    Run the following substeps in a loop,
    until the first step in the loop requires that the loop be broken,
    or until a step requiring the algorithm to fail is reached:

But the substep containing "break the loop" isn't the first, it's the third.

You could just change "first" to "third", but it would be safer to change
"the first step" to "a step". In fact, you could go further and merge the two conditions, e.g.:
    ... until a step is reached that requires the loop be broken
    or the algorithm to fail.