In SMP, rubber trees grow new holes eventually, but you can't see them appear until you reload chunk or relogin to game. If another player logs in, he can see chunks at that moment.
Mods:
Code
mod_BuildCraftCore 2.2.12, mod_BuildCraftFactory 2.2.12, mod_BuildCraftTransport 2.2.12, mod_IC2 v1.64, mod_ModLoaderMp 1.0.0, mod_RedPowerArray 2.0pr4d, mod_RedPowerCore 2.0pr4d, mod_RedPowerLogic 2.0pr4d, mod_RedPowerWiring 2.0pr4d