When a tender is loading either with water, or burnables it occasionally takes over your inventory that you are looking at, if you open a chest / etc hopper at the wrong time.
You need to re-open the chest/hopper etc at the right time to get your inventory display back.

See screen shots for 'what' happens.

Having trouble reproducing this. I wonder if it is a mod conflict?

@andrboot I think I have fixed this in the latest version. EntityIDs were being confused server/client side

tigerbird1 reports this is still happening in 1.3.1

Can confirm, happened last night briefly as well.

Some new notes: clicking on any items from the tender fixes the issue; it resets the inventory back to what it's supposed to be, at least for a while. They are ghost items though, because I could pick up a stack, but then it disappears.

Additionally, my inventory only required my to pick up one stack; however the transmutation tablet GUI (from project e) required me to pick up all the stacks before it reset. I haven't been able to check crafting tables or crafting stations(from TiC), but the divide might between blocks/entities with an inventory and those which just display an inventory in the GUI (but don't actually store any items).

If it helps, I have friendly shaders off, as it broke rendering for other things: for example, sand had missing textures on the certain sides, EnderIO machines' were completely borked (rendering-wise), etc.

EDIT: this is tigerbird1 from Discord.

Fixed in the latest test build, will be included in the next release.