Though, I should add, it's probably unexpected that this happens:
ABBBBBBABBBBBBB
That's because of an internal rule that says, if there are more than 6 notes beamed together, break the beam on the first beat, meaning 1/16 in this case since the time signature is x/16. (This rule is more likely to get triggered for, say, a run of 1/16 notes in 4/4, which will get broken up in groups of 4.)
You can always override the default beaming, but I suppose we could make the default behavior a little better by breaking long beams on the "middle" beat if they span multiple beats.