Shifter issues

So my b2600i runs and works great, I love it. But, (there must be a but) three times now a retaining pin between the shifter and transmission has fallen out at rather inopportune times. Every time it's happened I was moving from neutral to first, but that may just be coincidental. The shifter becomes loose and is incapable of engaging the gears. My mechanic fixed it no problem (and for free) but couldn't figure out what caused it and is totally stumped. My mechanic is great but I thought maybe he doesn't know b's too well or is high or whatever I dunno, so I took it to another mechanic, figured a second opinion couldn't hurt. (don't tell my mechanic I cheated on him) But alas, the new guy barely knew what I was talking about let alone could fix it. So I wonder is it something I'm doing while shifting? Maybe the pin is worn? I haven't driven it much out of fear it will happen again and strand me in a mud hole but now that summer's here in the Northwest I need it for transporting bikes and kayaks and other toys. I haven't looked at it personally yet as I was in an apartment, just moved to a house, maybe I'll take a look tomorrow. Anyone else have this problem?

The bushing that snaps onto the end of the shifter must have broken. Take it out and look at it. It could be half gone and spinning inside so it pops out at times.