If you use shift and down arrow to select a range, then let go of shift and just press down through other messages, it is not unselecting all the previous selection like it used to in Claws (and what is standard). Instead, it is unselecting just the very last message and leaving the rest selected. Doing the same thing but with the mouse acts normally/correctly. Very odd Noticed this in 3.11.1. I do not know when the bug appeared (since I hadn't updated regularly, nor have a done a regression test, but it is not present in 3.7.9).
*** This bug has been marked as a duplicate of bug 3321 ***