I am currently using the version 4.3.0-1944~g299bd908fc (on a win10-64)
I regularly export e.g. raw files to the TIFF format and each time I select another film roll (in the left panel) - the “target storage” under Storage options (in the right panel) will still show the path of the previous film roll.
It would be easier if the default target storage automatically changed to the path of the current film roll (imo) - Darktable must know the path of the next film roll and just need to copy it to the target storage field. I don’t know if other considerations are contradicting this - if so, I haven’t observed them yet.
Also the list with $( variables should be a selection-list and not just a viewing list. The list is very flimsy - and hard to keep open while reading.