Occasionally lines show up in IRC with just a user and no transaction info. This happens because we currently compare timestamps to get transaction info, and hope they're equal. This works for ~70% of cases, but fails, with timestamps being in the past or even in the future. I can easily reproduce this on phab-01.wmflabs.org by spamming comments on a bug and watching which transactions are found and which ones are missing.
On https://phab-01.wmflabs.org/T110: comment "eeek41" had an epoch of 1416804529 from feed.query, but in maniphest.gettasktransactions it reports a dateCreated of 1416804527.