When visualizing a program with three MapPartition operators that branch off from an OuterJoin operator, two of the three MapPartition operators are not connected to the OuterJoin operator and appear to have no input.
The problem is present in FireFox as well as in Chrome. I'll attach a screenshot.
Update: It appears that the problem is non-deterministic. I ran the same job again (same setup) and the previously missing connections were visualized. However, the UI showed only one input for a binary operator (OuterJoin). Running the job a third time resulted in a graph layout which was again different from both runs before. However, two of the MapPartition operators had not inputs just as in the first run.