A friend of mine found a Summon Swords scroll. The first thing we noticed is that you can cast it multiple times, and it keeps creating new swords. They don't seem to expire either, as he managed to cast the spell 3 times in a row without any of them despawning. This makes the spell extremely OP, and doesn't seem to be the intender behavior. I mean, the summon horse spell doesn't allow you to summon multiple horses, I would expect this to work the same way.

Summoned horse is a special case, this is how summoned are currently intended to function. Although, a summon rework is planned, as I agree it's not the best system. In any case, it's not a bug