Invisible Customers at the door. Impossible to slide a drink down bar

How on earth do you get support for the glitches in thid game. I mean there are invisible customers left at the door >> glitch << and I cant find any rhyme or reason as to how you slide the drink down the bar. There is no consistent way to do it and get it within the boundaries for success. Great concept Bad execution :(

financeqt1 about Claire's Bar, v1.7