Model export/save breaks module input and output options

After exporting/saving and re-importing a model containing modules, all module inputs and outputs become blind to new connections.

I would assume that export/save is broken, because I could make new connections to both inputs and outputs in modules contained in the "World2.sysdyn" sample model after importing it.

Reproduce:

1. download and import model attached
2. create a new input symbol and draw a dependency connection to one of the modules
3. choose the module, go to Inputs tab and observe how you can see the new input when choosing a "Refers to output" variable
4. save the model as World2saved.sysdyn, delete the model and import the saved model
5. repeat steps 2 and 3, this time the new input variable cannot be seen in the module

World2.sysdyn