Rakka is bothered by the fangirl in the thrift shop in episode 8. When Rakka runs away, the fangirl steps back, and her eyes double (11:24). This can only be seen by watching the scene in slow motion.
Notice that few frame before, the Haibane Fangirl blinks, but her face doesn't change. It means that her eyes were on separate drawings (so that the whole body doesn't have to be redrawn every time). But few frames later, she backs off as Rakka runs away from her. As Fangirl reacts, her whole body is redrawn in a different pose, including her eyes. Whoever composited the scene, forgot to "turn off" the column where her "floating" eyes were, and forgot to "preview" the scene before exporting it to the final editing...
murphy attempted to measure the heights of the Haibane in the show, but after some discussionOHBB it seems that the drawing is not always exact. For example, in episode 10 Washi is the same size as Kuramori, but in episode 3 he seems to be much taller than Rakka and Hikari.
The door to Reki's studio looks different throughout the show. At least 2 different designs were spotted. It even changes within the same scene.
Bidirectional studio door
In addition to the doorknobs constantly changing, the studio door's direction of opening changes when Rakka enters the, for the last time, to save Reki. This was spotted by Belthazar in his "Thoughts and Questions" threadOHBB in Dec 2003.