Key change at line break, unwanted key symbol at end of line above

In my current score I wanted the lines to have eight measures each, since that corresponds with the structure of my tune. I achieved this by hitting Return at every eight measures; I didn't find a smarter way. My tune started in the key of C, but from measure number 49 my tune should be in the key of F. I managed to get the correct ♭ key symbol at measure number 49, but for some reason that symbol also showed up at the end of the line above. That looks strange to me. See attached image. It's not a big problem, but if I can get rid of that unwanted symbol, it would be nice.