Help with Jc Shampoo/vac

[slash007]

I have a shampoo vac that has an issue I haven't seen before. When shampoo is selected, both the compressor and shampoo motor kick on. When the button on the handle is pressed, the relay for the shampoo motor activates and the shampoo motor shuts off. What would cause something like that? On my other shampoo/vacs, I noticed that both the shampoo and compressor relay activate as soon as shampoo is selected, then when the button is pressed, just the solenoid is energized.

Thanks.