No. Just be prepared to spend a bit longer going through immigration. In fact you might as well tell them about the problem as soon as you hand over your passport, so if they decide that they need to check in the back office, they have some idea of what they are going to find.
Agreed, and be very calm!
I would say that now they have had "eyes on" you and your documents it should be easier, and may already be solved (if you are lucky).
Although the paperwork was in order as far as you were concerned, they obviously still had a flag on you! It happens and it is normal. I would not let it put you off visiting, in fact if you get a regular pattern of in and out you will become unflagged even quicker as the agent dealing will see it as a waste of time, they obviously now already seem to be "no big deal" as you said in the OP.