Question about Mail Fetch/Push

So I have my mail accounts set to Push, however, I have 2 email accounts on my phone. My work email I have set to Fetch every 30 minutes. My personal account I have set to Manual. All during the day, I never have any problems with my phone keeping my personal emails until I manually check them, however, overnight something happens with my phone and I wake up with all my personal emails pushed to my phone!

Can someone tell me why it doesnt fetch my personal email during the day, but at night it fetches them when I dont want it to?

Its not a huge deal, but is kind of annoying...so when I wake up in the morning and turn on my computer, I have to not only delete my emails from my computer, but also duplicate emails from my phone.