There are a whole lot of reasons for tailing loops but, as Cliff said, dropping the tip of the rod from its oroginal path on the end of a cast is not one of them.
The most common causes result in a concave tip path as Cliff said. In order to HAVE a concave tip path, the rod tip must RISE at the end of the casting arc.
The most common causes of concave tip paths vary with the experience of the caster. For very experienced surf casters, for instance, the most common cause is too high a trajectory backcast (to get above the beach behind them) combined with too high a trajectory forward cast (to get the distance they need to reach fish). Most surf casters using full length lines are pushing the "180 degree rule" envelope with every cast. That's why most use shooting heads.
But for casters who are just rusty, but experienced, it is usually too early an application of force either with rod rotation or the haul or both - when going for more distance. They "hit" the cast too early in the stroke and cannot continue acceleratinig fast enough to prevent the rod from unloading too soon. So the rod begins to "unload" (straighten) while they are still rotating the rod through the cast.
This causes the concave tip path Cliff was talking about. And this is likely what the original poster was doing. If you start slow and accelerate the rotation through the cast, hauling late in the stroke, this will not happen. On distance casts, the rod tip will deflect downward to such a degree that it will nearly hit the ground in a 170 degree cast, as shown in the pic below of a 1950's world distance champion caster. He is not setting the hook there, he has just released the line on his forward presentation cast.