I don't really know for sure if it is a bug or not but while looking to solve a problem with ADs_Beta2 preferences update I found this:

system/language/admin.php
define("_MD_AM_DBUPDATED","Database Updated Successfully!");

Everything okay with all other modules. When DB is Updated it displays correctly.

system/language/admin/preferences.php
define("_AM_DBUPDATED",_MD_AM_DBUPDATED);

This does not appear to be correct??? But, I didn't change it because I don't know for sure as I am no php master.
But what I was getting in the Ads Beta2 module when updating the module preferences it displayed: _MD_AM_DBUPDATED

So I left the define in the preferences.php as it is since it says to not change. But I added below it:
system/language/admin/preferences.php

define("_MD_AM_DBUPDATED","Database Updated Successfully!");

So now it looks like this:
define("_AM_DBUPDATED",_MD_AM_DBUPDATED);
define("_MD_AM_DBUPDATED","Database Updated Successfully!");

The Database Updated Successfully! now displays for the Ads Beta2 module and everything else seems okay too.

But, still the question remains. Is this correct in the system/language/admin/preferences.php?

define("_AM_DBUPDATED",_MD_AM_DBUPDATED);

Quest

Normally it should be ok, as the admin.php language file should always have been included before the preferences.php file.

_MD_AM_DBUPDATED is defined in admin.php, then the constant is used in preferences.php file - no problem there.

The only explanation I can think of is if a module includes the preferences.php file from the front end without specifically also including the admin.php file... is that what's happening?

I dunno...