http://manicexpression.webs.com/apps/blog/show/40908214-a-look-at-sitcom-characters-ruined-by-their-own-shows

Miles

Miles was the neurotic executive producer who Murphy was constantly teasing. Of course that was because he was a bit young for the job. Miles was funny when he would freak out over stuff and attempt to control things going on around him. Then late in the run, they decided to have Miles run off and marry Corky. Suddenly Miles was whining about his marriage and stories with him became about that, and the character just lost focus. So much so that Grant Shaud up and left the series. He was replaced by Lily Tomlin, and while I love Lily Tomlin that was the point I stopped watching. This wasn't the only time this would happen on this show....

Murphy

When Miles left the show, it was still basically the same series. Then something happened to ruin that too! In the final season it was decided to give Murphy breast cancer. OK, that sounds like it could be interesting. Or it could be a lame excuse to get viewers. The problem? They watered down Murphy so bad, it wasn't even the same character anymore! Suddenly she is nice and soft spoken...when the hell was Murphy ever like that? The show should have quit when it was ahead.