Editing Kits: Object reference not set to an instance

[jmestep]

I've got this error message when editing a kit and was able to see what the problem was, but it isn't very clear and I don't think the interface should allow what caused it.
When you go to edit a kit part, an option in the kit part doesn't stay selected. For example, a kit part of blanket option twin size. If I initiate an edit, the twin size is not selected in the dropdown and I have to select it again or I get the error message. the dropdown should default to whatever size (twin) I'm working on.