I believe this only happens with the High Density and Two-Pane views.
All of the users in our GAL are in the "Last, First" format, and the summary view is trying to show a comma separated list of the members of the conversation, introducing extra commas.
If I had these users participating in an e-mail thread:
It would summarize 3 e-mails with 3 participants like this:
Bob, Jack & Jill (3)
And that's great. But our users are in a "Last, First" format:
So it looks like this:
Smith,, Ryan, & Roberts,
Hiri would ideally automatically detect this name format and make it look like the first summary.