Reproduced

1. Load editor without any text.
2. Press Bold button in toolbar.
3. Type somethign and press enter.
4. Deselect Bold and type somethign.
5. Notice that the Bold button is highlighted (but not applied, as expected).

Tested

Genymotion on Nexus 6P (7.0.0) and Nesux 5X (6.0.0)