Its possible to short stroke a push feed(partially chamber a round) then pull the bolt back and try to chamber another which would jam everything up good- atleast this is the best argument I've heard for a controlled feed and Ireally don't think its a very good one.

More likely to happen is to have a custom rifle build off a mauser 98 action (controlled feed) by a basement gunsmith or a hack who happenstohave a 'gunsmith' shop and find that the new chambering doesn't feed from one side or the other from the magazine- jamming it up solidly. Mauser actions have to have their feed rail and feed ramp geometry to be very precise in order to get the level of reliability that they are famous for. Unfortunately what often happens is thta Joe Huntergets his new mauser actioned rifle from the local gunhacker, goes to the range, single feeds it and is happy with the way it shoots, then takes it hunting. On a full magazine, the frst round will feed because it was on the same side of the magazine as being single-fed, but the second round will hopelessly jam the rifle up.

BTW: I'm a huge fan of the mauser design for a lot of other reasons than the controlled feed and prefer it over modern push feeds.