How to reproduce:
1. Open attached project "Steam Tools.zip" and scene "SteamworksExample"
2. Open Steam and log in to an account
3. In Unity enter Play mode
4. In Game View, click on "Find Match" button (a cube with your steam profile picture and name should appear)
5. In Hierarchy window, select "Cube(Clone)"
6. In Inspector window change Transform -> Position -> X and observe "Example Network Player Control (Script)" -> "Test Id 3" value

Expected result: the "Test Id 3" does not change
Actual result: the "Test Id 3" value changes to random characters

Reproducible with: 2017.4.16f1, 2018.2.7f1, 2019.1.0a9

Notes:
If the "Example Network Player Control" -> "Test Id 3" variable is commented out, the next SyncVar will have the same effect (in this case the "Test Id 2 will change to random numbers")