As you can see in bug 77018, I’ve been putting double comments in many bugs. That’s due to some kind of problem with the Preview feature in the review page. The normal workflow leads to a conflict window and if you ignore that and say “submit changes anyway” you get double changes. If you need more details let me know.
One question: How are you submitting your comments after previewing them?
I’m pushing the Submit button on the upper left corner of the preview.