In Minecraft 1.10.2 when holding something in the Off-Hand the shift-right clicking an item the item is not dropped to be picked. With the Off-Hand empty it works fine.

Mekanism-1.10.2-9.2.1.295

And 2 years later this is still an issue....

Should be fixed in latest release

Hate to be that guy who comments on a post from 4 years ago but this is still an issue / is re-broken in 1.16.5.

If you'd prefer I make a new bug report that's np, can do.

Honestly, I don't know. The ticket was closed, so I guess that it was fixed. The right-click stuff in Minecraft has changed a lot since 1.14 or maybe 1.12,