It seems that whenever a dependency does not specify an explicit flavor for a port which is flavored, portmaster reinstalls it unconditionally. For example, running "portmaster devel/llvm50" will recompile py27-enum34 and py27-sphinx, even though both are already installed in their latest versions.
I think portmaster should be modified such that when checking whether a port needs to be updated it first checks whether the port is flavored (probably using "make -V FLAVORS"), and if it detects that it indeed is changes the update check to be for the default flavor instead ("make -V FLAVOR" where the environment does not include the flavor).
There are quite many ports whose dependencies have not been marked (completely) with a flavor, and it probably should not be necessary given that a default flavor exists anyway (there were however a few commits where most of the flavors for python dependencies were added).
see also: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=227347
(In reply to Walter Schwarzenfeld from comment #1)
Sorry, this was paste error.
Should solved after ports r523835.
Thanks for committing the fix, it seems to work!