This has been an issue for a really long time now. At some point in the past, maybe around Season 3, a bug was introduced that made ships still be visible at the edge of the map after they had warped out. The ship would stick around for a second or two and the disappear suddenly. It's especially visible in cruisers, since they're big. This is annoying the hell out of me, especially since it worked before and it just seems so unpolished.

(I'm calling it a bug because I'm guessing it was unintentional, since it worked fine before that.)