I have been using the EBUILD_DEFAULT_OPTS="-atv" as this saves a lot of typing when exploring what to emerge next. But this causes some issues:
When running emerge --info I can't get rid of the -v.
Suggest: ignore -v from OPTS and use on command line if wanted.
When calling from script, emerge complains about -a.
Suggest: only complain if specified as "emerge -a", but drop silently if from OPTS.
When running emerge -p, emerge complains about -pa.
Suggest: only complain if both -p and -a specified in OPTS or cli options. If options are specified one in each source, the cli should be used.
Similar issue exists with --columns and -t.
Obviously, there was only one source for options when these messages were written.
We really need to rewrite all the option parsing to use python's optparse module. We will certainly consider these suggestions at that time.
This is fixed by now with --ignore-default-opts