Assignment does not work when prediction was active

Reported by Jürgen Graf (Uni HD) and confirmed by myself: He starts with a molecular structure and an experimental spectrum, and does an 1H assignment - everything works (see file attached). Then he would like to do with the same set of data also a prediction for 1H, and then perform the assignment. So, he opens the dataset (structure is already there) and clicks predict. [btw, at least for me the level of the simulated spectrum is strange - it is hard to recognize until you click 'same top']. Now, there are two spectra. If he tries to assign the (experimental) one, there is an error saying 'atom already assigned'