Copying a process model leads to unwanted labels in start node and edges

[junkerm]

Describe the bug
When copying a process model (copy --> paste as, not duplicate), the copied process model has strange labels in the start node and on the edges (undefined)

To Reproduce
Steps to reproduce the behavior:

1. Create a process model with start node and an activtiy and some edges
2. Copy the whole model (on the requirements page)
3. Pate the whole model (on the requirments pae)
4. Observe the result

Expected behavior
The copied model looks exactly like the original