Whenever I press Ctrl+Shift when in the urxvt terminal, the key combination toggles the ISO14755 mode of the terminal, letting you enter unicode sequences manually. I have personally never used this feature myself and just got tired of dealing with it as it would toggle on while I was trying to trigger a keybord shortcut of a different background process (i3wm).
urxvt has an way to disable the mode completely with the
iso14755 option. So I put the following into my
Then I reload the configuration
$ xrdb -merge ~/.Xresources
New instances of urxvt should no longer toggle the mode on Ctrl+Shift.