My sisters 87 truck has a strange problem: when it's in 4LO and you shift the transmission into reverse it kicks the t-case back into 4HI mode. It's not a let the clutch out and it jumps situation, it seems like there's an interlock that moves it with the shifting action. Is it supposed to do this?

It has a 5 speed manual (obviously) and auto hubs.

Thanks for the help!