AFAIK that's the way it is (at least it's the way we play). The highest combination counts, so if the highest possible combination is on the table, it's a split pot. There's no special rule for this case... which isn't really a problem, since it a) occurs very, very rarely and b) all players will naturally go all in, so that (aside from the blinds) the game is right back where it started.
In the case of a straight on the table you'd still want to play it out though, since one player might have a card that extends the straight upwards, so in that case there's really no need for a special rule at all. The round may still be interesting.
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