Water reasonably won't flow specifically into the Prewash compartment unless a prewash cycle function is selected. You can't be sure it won't work properly if you've never tried it. Water flow later through the main wash compartment and also passing through the prewash compartment is of no concern being that the prewash detergent would have already been used if said function had been selected.

I hope you are right dadoes. There should be two water inlets on that side if that is true. I don't know how to check that.

Take the top cover off the machine so you can see how many hoses/feeds connect to the dispenser drawer.

A Samsung WF330 (5 years old) I refurbed in February 2016 for my sister has four water feeds to the drawer. One from a solenoid on the hot water inlet connection goes to the main wash compartment (2). Three solenoids on the cold water inlet that go to the prewash (1), bleach (3), and main wash compartments (4). Presumably two of the feeds together merge for the softener compartment (don't know which two). A separate hose (5) tees off one of the cold feeds to the window washer nozzle. A diagnostic routine toggles the water flow through the four feeds. There's a fifth test for the water flow to the window washer nozzle but WF330 doesn't have a separate solenoid for that so the fifth test position doesn't do anything on it.

Your model may be arranged differently regards to the feeds.

What's your Samsung' s model number?

The model number is: WF337AAWXAA.