There is tremendous variation in toilets in the US, but the problem cited most often happens when the individual flush valve is worn out or not properly adjusted.

After flushing, the valve that refills the tank for the next flush diverts a small stream of water into a pipe to refill the bowl itself. If the bowl stream is too large, or if the valve doesn't shut off completely, the bowl will be overfilled, resulting in the unsanitary condition described. The condition may also occur if the prior flush was incomplete, and left more in the bowl than intended, but that's usually obvious.

Older toilets installed in private homes generally were fairly "tall," so the problem didn't come up too often. In the "neo-modern" era of the 40s, many people installed "modern toilets" that were "low and sleek like a new Buick" and the problem was quite common. Some of these had the rim of the bowl as low as 10.5 or 11 inches above the floor. You could conveniently rest your forehead on your knees while doing your duties, and handrails or a helpful very-good-friend might be required to get off of one - especially after a long reading session.

The advent of the "low-volume" toilet regulations a few years back resulted in installation of a great many toilets that didn't flush at all - or that required several cycles to clear the bowl. It is common to find various "tricks" used to increase the initial water charge with these, so the problem would be very common. Improved designs have eliminated the flushing problem in newer models, but a great many of the "early design" kind are still found in motels etc.

Standard designs in currently available "seats" come in 4 or 5 different standard heights, with the "comfort seat" being more and more popular. This style places the bowl rim about 16.5" above the floor, and the cited problem would be unlikely - especially with an effective low-volume flush model. Since the "high seat" is required in most places for the mandatory "handicap stall" builders often have put the same stools in all locations (quantity buying, and all that), so these may be found in many newer buildings, or those that have been extensively remodeled.

The best advice though, is that putting the seat down before you sit will get you an extra inch or two (of clearance, that is).

John