First and reverse are non-syncro. That's how that happens.
As harvester said, it is either the shift linkage not pushing it in all the way, the shift fork worn or there could be a problem with the detent or lock-out on the side cover.
The shaft of the shift fork can be loose but more likely they have wear on the inside of the fingers. The detent will hold the shift lever in position, if it is going all the way into the detent and gear.
Chipped corners on the teeth shouldn't hurt anything. It might make it slightly harder to downshift into first while rolling.
