This is a great question. I looked through all of the rules on betting and raising in the TDA rules and all I could find was the act of "pushing out" chips when referring to betting or raising. I saw nothing that covered forward motion with chips in hand. I have my own ideas about the act of "forward motion" and that is one of the reasons I am in favor of a betting line. Crossing a line on the table layout seems to be a more definitive action than using a judgment call, or raising the question of whether a player advanced his or her chips far enough to prevent a retraction.
I gave you my feelings in my long-winded version about the unclear action of the player described. The TDA describes betting and raising by pushing out...there is no mention of the player who picks up chips, moves forward, (sometimes with two fists full of chips) only to release a single chip! How far can he or she advance without being liable to complete their action? That is an excellent question. I have experienced different house rules in many years of playing. I have to say that I was surprised by some forward motion and release rules that I've experienced.
To answer your question with the limited knowledge of any other house rule that might pertain, I would have to consider that action as a call only. I'm not quite following your statement describing "go back & leave chips unrecognizable" but the deliberate forward motion with chips in hand indicates the deliberate intent to ack. A simple warning to all players before the game begins would be a good way to prevent future confusion. Example: "I'd like your attention please!" Make your intentions clear. When betting or raising, be sure to either announce the amount or push your complete bet forward in a single motion. If you pick up chips and advance them in a forward motion, you may be held liable to complete your unintended action!
Short answer...without verbal clarity or a release of the chips, I would force a call.
