Pinned message selectively not working

One of my friends in our private messages gives me his weekly work schedule so I have some idea when he's available, and we always pin it for easy access. One of the only times I use the pin feature in PMs. Recently, I've had two occasions where clicking on the most recent pinned message tries to quick scroll up to it, but then immediately throws me back down to current. And it does this consistently--when I said it's done it on two occasions, I mean two different posts, not two times ever.

I can get around this by clicking an older one first, and then clicking the newest one, that seems to work fine to get me there, but that's just a bit annoying, to say the least. I can't say if it happens anywhere else cuz I don't use the pinned messages anywhere else that frequently, but now that it's happened twice and wasn't just a fluke, I'm thinking that could, maybe, be a more widespread problem than I'd personally notice.