Yes, this one.
In fact, there are two things :
- adding/removing a panel to the Message notebook
- showing/hiding this panel
One command in the view menu is not enough to handle the different combinations.
In the code, the command clearly refers to the first choice and has nothing to do with "Is it visible".
To solve it, this item should be renamed to match better what it does and another should be added for visibility.
But continuing on this bug (or not) may lead to another post...
Dje