2008 KW T800.

I've never heard of a truck doing that. Although the previous owner could have plumbed the PTO valve into the suspension dump circuit. Reason likely being that they pulled a dump trailer or something and an air ride truck is less likely to tip over with the suspension dumped vs inflated.

 

It's not a problem. It was likely plumbed that way for stability reasons.

 

Used to work for a company that had several 2007 & 2008 T800's and they all pulled Trail King "hydraulic tail" step-deck trailers. There was a valve on top of the airbags that would open when the PTO was engaged and that would dump the air on the tractor thereby increasing the ramp angle on the tail. However, the trailer also had a dump valve so the entire combination could be dropped several inches to get the ramp angle as low as possible.

 

That's a very common way to plumb systems as described when pulling particularly dump trailers to eliminate the need for the driver to remember. It's a very simple move simply T into the air line going to the PTO on the raise side and run it to the dump valve supply side and T into it there. Very handy feature and really no downside to it at all.