SetPlayerCustomProperties called from Start() has no effect

Options
Whenever I join a server, I get automatically loaded into a new scene (automaticallySyncScene=true). Once the new scene is loaded, a Start() event is triggered which calls SetPlayerCustomProperties. If I check the player.CustomProperties right after the call to SetPlayerCustomProperties in the Start() event, everything seems to be fine and the values seem to be properly updated. However when the Update cycle starts running, the player.CustomProperties seems to reverts back to the values that were set prior to the SetPlayerCustomProperties call from the Start().
Why does this happen?