Document can not be unloaded in some cases

Scenario to reproduce:

1. Open "data/samples/Genbank/murine.gb" and "data/samples/Genbank/sars.gb" as separate sequences (in different views).
2. Select these two documents in the project view and unload them. Agree to close views.
   Expected state: both documents are unloaded, there are no errors in the log.
   Current state: only one document is unloaded, there is an error in the log: "Document 'murine.gb' can't be unloaded: Document is locked by some algorithm and cannot be unloaded"