Factorio Forums

It's showing as an available tech, but requires blue science (I have none yet).

http://imgur.com/gPWPA0W

I'd say not a bug : it only needs Electric distribution 1 to be researched. it can need science 1, 2, 3, 4, but there is only one technology that's needed to have it available.
If you get a close look, (almost) no tier 4 science have Alien tech as a prerequisite.

When you look at the colour scheme, it's clear that green is for done, red can't be done, and yellow for available. No other item in that section is currently unavailable due needing as yet unreached tech levels. Perhaps this should be changed, having non available tech show in the available part section kinda defeats the point if we're being honest here. Otherwise why have sections in the first place

This is not a bug, more of a feature request.
This can cause problems with mods. We will see how to solve this in 0.13.