Operating system: Ubuntu 18.10
Graphics card: Radeon RX 560 Series (POLARIS11, DRM 3.31.0, 4.18.0-18-generic, LLVM 7.0.0)
Broken: 2.80, ebc44aae9897, master, 2018-05-11
Short description of error
Cached frames become invalidated as soon as another video strip is selected.
Exact steps for others to reproduce the error
Add two video strips, one above the other. Select one of them and play, to get some frames cached. Then select the other strip and parts of the cache becomes invalidated.