[1.2 - 2.5.5]
With your default configs the leave blocks have an extreme flickering effect (rendering errors. No optiFine or like that used)
Going to weather ez2 config ingame > advanced > disableMipmapFix > true
and the flickering is gone.
But as it seems that option is not stored in the cfg files how can i distribute that option being disabled when delivering a modpack ? Just add the 2 dat files in the config folder too ?

It is stored in the config, the advanced gui stuff is all stuff from config files, it changes the config files live, the specific setting you need for the file is: disableMipmapFix in CoroUtil.cfg in config.