What happens, is that development is not stopped completely with the use of a water rinse before fixing. There is nothing really "wrong" with this method, but you may need to adjust your development times because of this.
An advantage for using a water stop is that development will continue most in the shadows, giving you a method of control for shadow detail. Can be done with paper as well, but not all respond well to this method.
The recommended procedure with a water "stop" is drain the tank, refill with water, agitate for 10 seconds, pour out, and repeat for one minute or five cycles. Sheet film, wash in a running water tray for a full minute, drain the sheet then fix.
Glacial Acetic Acid is dangerous to work with, so don't get it on you or breath the fumes and pour the acid into the water not the other way around. For films start with 28% Glacial Acetic Acid, mix 100cc for each 1/2 gallon use for 30 Seconds. There are other buffered formulas that are better, with less risk of pinholes. White vinegar can be used 1:4, but I would not use it for paper as you run the risk of discoloring the print as vinegar is not as pure as glacial.