Some days ago I noticed that some keyboard shortcuts which include the Alt key don't work anymore.
Windows Explorer: Alt+↑ (one directory up) doesn't work, but Alt+← and Alt+→ (one directory back/forward) do.
SciTE: Access keys in the Find/Replace dialog are working for "Find Next" and "In Selection" but not for "Replace" and "Replace All" (access keys bold).
Windows UAC: When asking for administrator privileges, the dialog's access key for No ("Nein" - German language pack) works, that for Yes ("Ja") doesn't.
What could cause this behavior and how do I get rid of it?