DNS behavior question.

[danjourno]

I'm no expert when it comes to DNS so forgive me if this seems a
stupid question.

Yesterday one of my sites had a dns issue.. i think the servers went
down. I couldn't get on to the hosting provider where the dns was
hosted for over an hour so I redirected my domain to backup
nameservers.. which also pointed to a new host server for my website.
I left it like this for about 3 hours until the dns issue was resolved
and then changed the domain to point back to the old nameservers and
hence the old host server.

Anyway.. what I'm confused about is the behavior.. When i made the
first change to point to the temporary nameserver and the initial
nameserver was down the results were more or less instant. Whereas
now, after I have switched it back I am still getting half of the site
traffic going to one host server and half to the other almost 24 hours
later. Is this normal behaviour?