Resource calendar hour mistake

Hi!

On project for the web i've created a calendar template from a "calendar resource" and assigned them a 08:00 AM - 17:00 PM GMT+1 working hour

Then i assigned this calendar to each resource.

I have some plan on project with these resources but when i assign them some task the hour are "random", why?

This cause daily hours counting mistake

Start date: 5/7

End date: 5/7

Total should be 1 day(8 hour) instead of 0,75 day

What am i missing?

Thanks!