I'm pretty sure what you're describing is this long-standing bug[1] I've experienced only when using Mobile Safari on Reddit - affecting both old.reddit.com and the (horrible) modern Reddit. It just doesn't happen in other browsers/engines except on iOS. It's especially annoying on an iPad when I tend to use back/forward instead of open-in-new-tab-then-close on iPhone.
[1] At least, I hope it's a bug.