You have got to be kidding me.
Anyone with a bit of common sense can see this is an obvious bug.
Every suggestion in this post is an unacceptable workaround, and to blame the buttons and say this is by design is simply a joke.
If you have a property called IsEditable on a control, it can only mean one thing; Either the control is editable or it is not, there are no middle cases here.
We are in the middle of 2015, 6 years after you initially (correctly) confirmed this to be a bug.
These kind of situations are what makes potential customers stay on the fence..
Please take notice.. Jonathan.