troubleshoot C-M-/ key binding (dabbrev-completion)

[Michael V. Antosha]

Hello,

Key binding C-M-/ (dabbrev-completion) does not seem to work for me.
Could someone point me in a right direction to find the cause of this behavior?


Details:

1. dabbrev-completion works fine if used explicitly (M-x dabbrev-completion).

2. M-/ (dabbrev-expand) and C-/ (undo) both work as expected.

3. Using C-M-/ (i.e. pressing Ctrl+Alt+SLASH) seems to have the same
effect as M-/ (dabbrev-expand).

4. Other C-M-... combinations seem to work fine.

For example, C-M-\ (indent-region), C-\ (toggle-input-method) and M-\
(delete-horizontal-space) all work as expected, each doing its own
function.

5. From the output of describe-bindings (C-h b):

    M-/             dabbrev-expand
    C-M-/           dabbrev-completion
    C-/             undo

    C-\             toggle-input-method
    M-\             delete-horizontal-space
    C-M-\           indent-region


Any hints?
I want to find out what is wrong with my setup
(and how to troubleshoot -- step by step -- similar issues with Emacs).

Thank you in advance!

Best regards,
Michael


-- 
Michael V. Antosha