How to reproduce:
1. Open any project
2. Create a game object and add a child game object to it
3. Set Static = true on both game objects
4. Select the parent game object, click on the drop-down next to the "Static" checkbox and remove one of the Static flags
5. Observe the message - a number is shown instead of the name of the flag ("StaticFlagsMessage.jpg")

Expected result: pop-up message "Do you want to disable the Lightmap Static flag for all the child objects as well?"
Actual result: pop-up message "Do you want to disable the -127 flag for all the child objects as well?"

Reproduced with: 2017.3.0a1, 2017.3.1p2, 2018.1.0b9, 2018.2.0a2
Not reproducible with: 2017.2.1p4

Fixed in: 2018.2.0a4