Thanks for the report, I can repro when the snapshot is run before DT on DT is opened.  It's also reproducible with a small HTML page loading a single worker with a single log.  Your guess seems to be correct, alph.

The first message with the correct 'HeapSnapshot.js' anchor is generated from _onConsoleAPICalled, while the second incorrect message with 'Trie.js' comes from _logEntryAdded.  It looks like "buildSnapshot" method is called only once, but we incorrectly log the message twice instead of once.

After discussion with kozy@, we seem to store messages in both the Worker's store and the Page's store.  I think an appropriate solution is to prevent these duplicates from being logged, and investigate whether there are other cases when a LogEntry is generated by the incorrect target.