Guys even leave LEO jobs for other LEO jobs, oftentimes as lateral moves. The gaining agency doesn't frown upon it, and the vast majority of losing understand that it's the cost of doing business. So long as, whether going to another LEO job or not, the person in question follows the appropriate or legal or even accepted methods of quitting (the 2 week notice thing, or whatever is required), then nothing should be held against him/her at all.