I have a very nice Yugoslavian M48 rifle; the bolt does not stay open after the last round. The follower looks to be unmodified and without a stop, can someone tell me if this is the way these rifles were produced, or if mine is modified?

Mausers have both types of followers; you can change it out if you want the bolt to not close. All German 98s have the squared off follower; many other makes and contract rifles have tapered ones. Don't matter either way. I have one totally original Yugo 1924; it has a tapered follower.

My M48 and 24/47 both have "tapered" followers

Thank you, I shall leave it as is.