Hi Jennifer,
We experienced the same situation with hours entered on 1/31 for the previous week.
The user noticed it when he toggled between the All timesheet view - that showed total hours entered and then the individual timesheet. The view showed 42 hours but the timesheet showed close to double the hours by day and those individual entries were duplicated when going into the hours in the project - but strangely enough not every record was duplicated about 90% of them were. I entered in a support ticket - the problem could not be re-created by WF. My concern was similar to yours as we may use these hours for billing or just comparing budget vs actual.
I created a journal entry report to track down all the hours entered in that particular day to see if other users experienced the same issue - I didn't look like it happened again but I haven't looked further as it is difficult to see.
It is very inconsistent.
We use Chrome typically and the user was in Chrome when this happened.