Georg: In response to your post about "String Bets" (which I think should be a separate topic from "Betting Line"), the TDA has a series of rules regarding "Play, Bets & Raises". These are rules 29 through 36. IMO, the situation you describe is best covered by rule #30 which says, "In no-limit or pot-limit, a raise must be made by (1) placing the full amount in the pot in one motion; or (2) verbally declaring the full amount prior to the initial placement of chips into the pot; or (3) verbally declaring "raise" prior to the placement of the amount to call into the pot and then completing the action with one additional motion. It is the player's responsibility to make his intentions clear."
I agree with your interpretation. In the absence of a verbal declaration, prior to chips going into the pot, I would support the dealer as well. Players can always ask for "Time", if they need it to figure out what they want to do or how much to raise or they can use option (3), announce the 'raise', place the chips needed to call into the pot and then, in one additional motion (which might take a few additional seconds), place the full raise amount into the pot.
Hope this helps!