Do reviewers become biased about research papers written by authors of a previous low quality paper?
I would distinguish between two papers in parallel (as in your example) versus a history of bad papers.  

If I'm seeing a good paper and a bad paper that share an author, and I don't yet know that author well, then the bad paper probably won't affect my opinion of the good paper too badly (unless we are talking really embarrassingly bad).  I'll have a mixed opinion, but I'm still forming it.

On the other hand, there are certainly some authors who have built up a history with me such that I see their paper and think: "Oh no, I hope they've learned from last time."