Hello,
first of all, sorry if this is not a bug but a sought behavior. I just report here because current behavior "feels strange" -for me-. In Sell/Sack screen, MMB response fo the inventory entries is different whether object needs research or it's just added to UFOPaedia without researching, no matter if the item has been already researched....but peeking at the code I found that pressing Ctrl + MMB at researched items, they are shown in UFOPedia.
It's strange, because the different behavior of researchable or not-researchable items -first ones need MMB-Ctrl; second ones only MMB).
I will suggest "flip" Ctrl use, so when pressing Ctrl+MMB you go to Tree Tech Viewer, and only with MMB you go tu UFOPedia entry for all known items (researched or not researchable).
It would be just change in "Sellstate.cpp", line 961 : "if (selectedTopic && !ctrlPressed)" to "if (selectedTopic && ctrlPressed)"
Thanks!