Do stable packages require stable dependencies?

Is there a rule or something else in the way Gentoo is set up that
requires/states/recommends that for a package to be marked as stable
it is a requirement that all dependencies also be stable?

If someone has a basically stable system and can take the time could
you possibly try

emerge -pvDuN rstudio

and see if it's trying to pull in lots of unstable haskell packages to
build rstudio-0.98.490-r1?

I've had to mask the stable version and use 0.98.490 for quite a long
time but I'm wondering if I have something misconfigured that' s
causing this.

Thanks in advance,
Mark