Did you figure this out?

I believe you're running into behavior I have also seen.  Consider the following scenario.

In an otherwise empty buffer, enter the following three non-blank lines (blanks here for readability):

Test1String
TEST2STRING
Test

Run the following tests, each with the cursor at the end of the third line.  (It does not matter if there is a newline after the third line.)

Firstly, invoke M-/ and what you will get is Test2string.
Secondly, delete the third line and replace it with "TEST1" before invoking M-/ and what you will get is TEST1STRING.
Thirdly, delete the third line and replace it with "test2" before invoking M-/ and what you will get is test2string.

I don't what this case-matching behavior is called, but it catches me occasionally too....

Cheers,
Mark

From: help-gnu-emacs-bounces+ludwig.mark=siemens.com@gnu.... [mailto:help-gnu-emacs-bounces+ludwig.mark=siemens.com@gnu....] On Behalf Of C K Kashyap
Sent: Friday, July 20, 2012 12:06 AM
To: Jambunathan K
Cc: help-gnu-emacs@gnu....
Subject: Re: dabbrev-expand ignores case sometimes

hmmm I am pretty sure its not M-I M-i or M-c . It's only M-/ and it simply expands in an unexplainable manner.

Regards,
Kashyap
On Thu, Jul 19, 2012 at 9:31 PM, Jambunathan K <kjambunathan@gmai...> wrote:

Can you be more specific.  What is the guarantee that you haven't typed
M-l, M-u or M-c?

> I have not customized dabrrev ... I believe I run into this
> accidentally when I type in some control/alt combinations
> inadvertently.
>
> Regards,
> Kashyap
>
> On Thu, Jul 19, 2012 at 7:34 PM, Jambunathan K <
> kjambunathan@gmai...> wrote:
>
>     C K Kashyap <ckkashyap@gmai...> writes:
>
>     > Hi,
>     >
>     > I noticed that at times when I do a M-/ and try to complete a
>     word
>     > that already exists in the buffer (I assume, this is what I
>     need to
>     > do if I need to do what I did using C-p or C-n on vi), the word
>     > completion happens but with weird casing. Sometime all caps
>     etc. I
>     > wonder if there is some setting I need to do when I get into
>     this
>     > situation.
>
>     Have you customized dabrrev?
>
>     See (info "(emacs) Dabbrev Customization")
>
>
>     >
>     > Regards,
>     > Kashyap
>     >
>     >
>
>     --