The UI for rockets can sometimes display data for one rocket when another is selected.
On the screenshot, you can see the right rocket (selected one) with an empty liquid cargo module. It is empty as you can see both from the mouseover tooltip and from the bar rendered on it in game world. The rocket UI shows it with a partly filled liquid cargo module and with an artifact module - those two belong to the rocket on the left.
The selected cargo module is one from the right one. This can be confirmed by looking at rocket's name: both mouseover tooltip and rocket UI show the name of the rocket on the right.
The rocket UI shows correct data for selected module - the (not shown) storage data below will show the module as empty. It's just the rocket summary thing that is linked to the wrong rocket.
1. Construct a rocket with an artifact module. 2. Send it on a mission and then back. 3. Without save+load, construct another rocket, this time without any artifact modules. 4. Select the new rocket. 5. Look at the UI, which will now be showing artifact module as present, when the selected rocket doesn't have one.