Rep comments missing?

I suppose it could just be a coincidence but it seems unlikely.

In my control panel I only get a comment on every other reputation line. At first I thought it was just a coincidence but now it's getting to the point where that seems highly unlikely.

I have 13 "lines" on my reputation list. The first line has a comment, then the third, fifth, seventh, etc. It seems strange that only half of them would lack a comment, and in such perfect symmetry. It seems more likely that there's something wrong with the list.

Has anyone else noticed this? If nobody else has this problem I guess it is just a coincidence after all.

I have 6 reps; 2 and 5 have comments. I think simply the users are not putting in comments when they pos/neg you?

Comments are required for leaving neg rep (although just putting in a period is sufficient, which obviously defeats the purpose), but positive rep requires no comment.