Fuel items showing in Filtered backpack, but otherwise inaccessible

I decided to move my stash of plant-derived materials from one box to another, the latter nearer to the Excellent Cooking Station in Sylvan's Cradle. I loaded my companion with the heavies, rummaged around some more, then went to the second box and accessed my companion's inventory.

It was empty, except for her usual clothes and axe. I searched around and discovered that, accessing the fuel compartment of the Cooking Station or the Alchemical Boiler, the 300 wood bundles, 700 sticks, 500 crude fibres etc. she had been carrying were now listed in the "Filtered Backpack". However, there was no apparent way to move them anywhere else from there. They also did not show up in my backpack, in case you're asking.

I tried ending the game to see whether that might recover anything, but, while the game's screens disappeared, Steam still showed the program as running. Activating "Stop the game" did not make a difference, at least not for a while. I then stopped the Steam-client, which, too, at first did notseem to work, but eventually did. Restarting the game duplicated the whole behaviour, reboting the computer made no difference.

As far as I can see, this behaviour now applies to all stations requiring fuel, potentially rendering the game unplayable from the point on where the fuel in any particular fuel compartment is used up. However, the time left to burn exceeds one hour on all of the stoves etc. I have checked so far, so that will not become problematic immediately.