Bookings on Blocked Nights

[Laurie-and-Lawrence0]

I have recently gotten two instant bookings on nights that I had blocked.  The first one was in the middle of a week that I had the whole week blocked out. The second one was for 10 days and began with five days that were not blocked and then went into a week that I had the remaining five days blocked. I didn't want to cancel on the guests that had instant booked so I've worked it out, but I'm unsure how someone booked on my blocked nights.  Yes...I've checked and the nights truly were blocked!  My only option is to change my bookings from instant book to where I have to approve them first, which I think may reduce my nights booked.  Anyone else have this problem???