#1 reason why 3.x should never have been written, IMHO: player entitlement. The idea that the DM is beholden to same rules as the players is, IMXP, completely new to the third edition.
(Edit: Much of the following assumes access to the 3.0 DMG as I am not familiar with the 3.5 version).
I never had this problem. Nor, has anyone else that I personally know. I don't doubt it exists, because it comes upon the internet. However, it tells me that either:
a) there exists players that are selflish thinking of themselves and not the good of the campaign (a player problem)
b) many DMs are too afraid to tell their players no (which is a problem with the DM- not the game) ; and/or
c) the DM didn't read the DM guide, because the 3e DM tells the DM that is ok to deviate and make changes. From the 3e DMG :
- "Let's start with the biggest secret of all: the key to Dungeon Mastering. (Don't tell anybody, okay) The secret is your're in charge" (3e DMG/ p.6) and "You decide how the rules work, which rules to use, and how strictly to adhere to them. That kind of in charge" (3e DMG/ p.6).
- "Good players will alway recognize that you have ultimate authority over the game mechanics, even superceding somethng in a rule book" (3e DMG/ p.9)
I can't even believe we had a thread a couple years back on whether a DM could "cheat" or not.
And, the answer to that question is in the DMG.
"Do you cheat? The DM really can't cheat. You're the umpire, and what you say goes. As such, it's certainly within your right to sway things one way or another to keep people happy or keep things running smoothly." (3e DMG/ p.18)
It is absolutely ridiculous for me, as a DM, to be expected to adhere to a player's expectations from meta-knowledge.
Then don't adhere to hit. If a player has a problem with it, take a rolled up newspaper (or the DMG) and smack them on the nose. Then, if necessary, show them
a) Rule 0 in the phb;
b) the above sections from the DMG; and
c) the following sections in the DMG:
"Every rule in the Player's Handbook was written for a reason. That doesn't mean you can't change them for your own game" (3.0 DMG p. 11); and
"As DM, you get to make up your own spells, magic items, races, and
monsters!" (DMG/p. 11) (emphasis mine).
(Or , just show them the door and avoid battery charges).
In my game, monsters have powers that aren't listed in the MM, and it has always been thus.
And, there was nothing stopping you from doing this in 3e. How does the player know that this is not a new monster specific to your setting, that you didn't put a template (WOTC or otherwise) on it , add a class, or whatever. They don't!
The "permission" to make changes was in the DMG all long, you either didn't see it or chose to ignore it.