Guillaume,
If you do see someone saying "raise 50,000" while pushing the exact amount of 50,000 with no reaction from the dealer or the player's, then they need to be corrected. There are many, many circumstances when your interpretation of the understanding of raise is intended to be be...just what you said, a raise to the total spoken amount. When I deal no limit, and a player announces his raise I like to freeze the action of the next player until I have clarification on the intended amount of the raise. I know it sounds difficult but after years of dealing it becomes "second nature" and you can almost feel what the raiser wanted to bet. Player A bets 500. If Player B says raise 1000, it brings the total bet to 1500. The problem is when the next player says raise again...this is when the clear intent of the original raiser has to be sorted out.
We need to teach the players, as well as the dealers, that if they do not make their actions perfectly clear, there are consequences.
One more note for clarification. If Player A bets 500 and the next player wants to raise to 1500, he must either push 1500 into the betting area, or say; raise TO 1500, (which translates to 1000 more), because if he says raise 1000 it would be understood to be 1500 and not 1000. I hope this makes sense.