That's odd for a variety of reasons. The stay bushing sits inside a ring in the linkage, which holds it up. Around the bushing are a couple o-rings to keep it snug. Underneath is snap ring to keep it from being pulled out. Inside there is a pivot bushing held in place to the shifter with a dowel. The pivot bushing should fit very tightly and slightly expand the stay bushing. It is difficult to pull out.
For your stay bushing to just fall out it would have had to been installed with no o-rings, the snap ring would have had to have broken and fallen off, the shifter would have to be lifted, and the pivot somehow be forcefully separated from the stay bushing.
Perhaps it was installed improperly.
35035 bushing
35087 o ring
062620210 o ring
031524000 snap ring
35035B pivot bushing if yours is no good
099910190 lock wire if you feel like using one, I don't