Caps Lock affects Ctrl+keys

[Yuri Khan]

Hello list,

I notice that, when I turn on Caps Lock, all Ctrl+letter combinations
behave as if I pressed Ctrl+Shift+letter. My expectation is that Caps
Lock should not affect any control modifiers (Ctrl, Meta, Super,
Hyper), but should affect normal character input (no modifiers or just
Shift) and might affect higher levels input (Level3, Level5 and any
combinations thereof with or without Shift).

$ emacs -Q

M-: (read-key) RET
press Ctrl+z
# 26 (#o32, #x1a)
(so far so good)

M-: (read-key) RET
press Ctrl+Shift+z
# 33554458 (#o200000032, #x200001a)
(ok)

M-: (read-key) RET
press Caps Lock to turn it on
press Ctrl+z
# 33554458 (#o200000032, #x200001a)
(expected: 26 (#o32, #x1a))

M-: (read-key) RET
with Caps Lock still on
press Ctrl+Shift+z
# 26 (#o32, #x1a)
(expected: 33554458 (#o200000032, #x200001a))

This is on GNU Emacs 24.3.1 (x86_64-pc-linux-gnu, GTK+ Version 3.8.2),
in Ubuntu 13.10, GUI mode. (In -nw mode, I get 26 no matter whether
Shift is pressed and/or Caps is on, which is understandable because in
that mode the terminal emulator handles all keyboard input.)

Does anybody else observe this? Should I report a bug? Is there an
easy workaround?