Reopening the session may show "This file is not part of any project" yellow label

To reproduce:
1. Open Creator project inside Creator
2. Open "operation.h" file
3. Close Creator and start it again. Reopen the last session
4. "operation.h" file is marked with "This file is not part of any project" yellow label. The label doesn't disappear, even when parsing C/C++ files finished. If you close this file and open it again, the label is not visible anymore.

Having yellow label visible influence e.g. "follow symbol" functionality, which is broken when the label is visible.