It Drives Me Nuts Everytime I See It

In the Book Sleuth section of abebooks.com, where readers ask for help in identifying half-remembered books, someone posted a request that includes this passage:

In 1996-97 I read a non-fiction book about a man who was diagnosed with terminal cancer. He was written off by his doctors but refused to go quietly. In his hospital bed, everyday, he would imagine the cancer shrinking in his body. He did this everyday for hours, laying there and focusing on the cancer cells shrinking to nothing.

This is a solecism I am seeing almost, well, every day. Everyday is one word when used as an adjective, otherwise it's two words. In other words, it's "everyday low prices" but "low prices every day." A distinction worth observing, I believe.