Unity won't save Cache Server Mode on restart if set previously to 'Local'. Additionally, console will throw out these errors:

Socket: connect failed, error: No connection could be made because the target machine actively refused it. (0)
connect failed
Couldn't connect to Cache Server.
Unable to connect to host localhost:62785.

Note: Port is randomized on each instance.

Reproduction Steps:
1. Open attached project "CacheServerDisable".
2. Open Edit -> Preferences and switch to "Cache Server" tab.
3. Set 'Cache Server Mode' to 'Local'.
4. Restart Unity.
5. Set 'Cache Server Mode' to 'Disabled'.
6. Restart Unity.
7. Observe that 'Cache Server Mode' is still 'Local'.

Reproduced with: 5.5.0f3, 5.5.0p2. 5.6.0b3