Staff Response Some Mounted Players able to block my character, but 99% others I pass thru??

Majority of the time when I encounter a player's horse, wagon, or a mounted player we seem to pass through one another...but during the past few days I have had multiple occurrences of mounted players who are able to stop my character's movement, and who make an obvious attempt to do so -- latest was two individuals blocking my travel on a road (I was on foot), and they continually rammed me until I switched server.

My question: why do I pass through majority of mounted players, or players driving wagons, as well as parked wagons and horses with no sign of impact or hindrance...but some are able to choose to run into me and block my travel? Am I seeing a bug/glitch/exploit of some sort? I rarely use horses, so I'm not at all familiar with what can and cannot be done with them.

Thank you for your time and assistance.