It's been mentioned a few times ( not sure about on here, but it was mentioned almost immediately on the discord when the public patch went live)
Hopefully, It has also been addressed already, But I cannot swear to that, as I'm not in a position to speak for the team, But *uses magic 8 ball* signs point to "quite likely"
You can avoid this issue by Not selling to Sword Specific customers (They specify the type of guard, grip, and blade they want)
If they see you holding anything that is not the sword they requested, they start to spawn the guard they requested under the shop
again, expectation is that this has been addressed
There's also a problem you may also run into, With shield customers, or multi-item - If they ask for more than just the tool, (like a tool and shield) serving them EITHER ITEM will make them believe they've left, and cause a 2nd customer to spawn when they actually do leave (dismissed after one or completed with two)
This stacks infinitely, and eventually will become impossible to have customers leave.
again, Can be avoided by dismissing immediately, customers requesting for more than just "one item"