Take the bolt out of the rifle and examine the bolt sear edge carefully.
See if it looks like it's been trimmed back a little. Also check the trigger sear viewable in the channel of the recv'r for the same problem.
Either one or both of these surfaces worked over and shortened some will allow the bolt to hold the cocked position just a little forward of it's factory intended position.
That will then put the small cam slot in the cocking-piece out of allaignment with the wing safety,,so you can't engage the safety. But the rifle still appears to cock and fire OK.
A non-matching cocking piece and/or wing safety that don't quite line up dispite being from the same Model Mauser can also cause the problem as mc points out.
Spanish Arsenal made Mauser parts from the 93 most probably fit but may make for less than a perfect union.
