I did some trickery to get it to work. There might be an easier way, but I created the property node in the main VI and wired the box reference to it, then copied and pasted the property node into the subVI. I created a new control from the reference input to the property node and replaced the other drawable control with the new reference control. Now everything is working properly. Thank you so much for your help Clint!
Take care,
Amanda