To reproduce:
1) Create new project
2) Make a prefab out of any object in scene
3) Select same object in scene
4) Change something (for example, Scale) to make it different from base Prefab
5) Click Overrides
6) Select the bit that you changed (if example used, Transform)

Expected: Comparison view is opened in full detail and size
Actual: Only a top bar (and sliding/malformed depending on how the compared piece is selected) appears

Reproduced in 2018.3.0b10, 2019.1.0a11