Going over the champion limit in TFT

Unfortunately I failed to take screenshots (thought windows + prnt screen would work...), but I was able to go above the champ limit in a TFT game this morning, by having a full bench and drafting a champion on top of that. I was level 5, with 6 champions fighting, and the additional synergies activated. As soon as I cleared a spot on the bench, it was filled up by the extra champ on the field, my team size went back down to 5, and the additional synergy disappeared. Is this normal behavior or is it bug? I thought having one champ too many on the field meant that one automatically disappeared at the start of a round, for the duration of the round.
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