Operating system: macOS Mojave 10.14
Graphics card: Intel Iris Graphics 6100 1536Mb
2.79.7, date 2019-02-06 14:18, hash fccf506ed7fd
In the texture paint mode preview window shows nothing. In case I start painting an press Cmd+z (ctrl+z for windows) the system freezes.
no special actions needed. the problem reproduces just always.