Steps to reproduce:

1. Open blue Ocean Pipeline editor
2. Create a stage named "Test"
3. Rename the stage to "Platform 1"
4. Add a parallel branch to that stage name it "Platform 2"
5. Click first first branch of parallel again

Expected:
Option to change the name of the stage to "Test"

Actual:
Changing displayed name will change the name of the parallel branch, but not the name of stage.
There is no way in the editor to change the name of the stage without deleting all parallel branches first.