1- Use a letter to jump/sort through files/folders until it loops back to the first file/folder. 2- Use another letter. Result: It doesn't work after the loop (unless you're pressing the same letter before the loop).
Can you confirm that type-ahead works for the second letter if you wait several seconds? (This looks like https://bugs.kde.org/show_bug.cgi?id=424416 )
Confirmed. *** This bug has been marked as a duplicate of bug 424416 ***