Why is there paint on my mirror?

When we purchased our home, the previous homeowners left a huge, framed mirror on the wall hung horizontally, as though a dresser should be beneath it. Up until last year, we left the mirror where it was and put our bedroom dresser below it. However, decided sometime last year to do away with our dressers in our master bedroom, and instead put in two giant wardrobes with deep drawers for easier clothing storage. This left the question of what to do with the mirror?

My hubby took the mirror and turned it on it's side and installed it on the wall as a full length mirror. He had to take the framing off of it to make it fit. This was ONE YEAR AGO.

Yes, that's the glue that surrounded the mirror from the framing. And, yes, it stayed on their for over a year, just waiting for someone to scratch it off. It's one of those things that I see so often, I forget it's there. Until one day last week, when our youngest asked why we had paint on our mirror. I was like, "huh?", and when he showed me, I was dumbfounded - has that really been that way this whole time?

So, very proud of myself, I got out a hand-dandy scraper and scraped it all off nice and clean. This brings me to having two issues....

1. How many things do I walk by that need to be fixed and I just don't notice?

2. Why hasn't my husband fixed this yet? :)