When I use the Multisport function on my 920 with Garmin Connect, the totals don't add up on the Connect site. The site reports both the Multisport activity as a single line item and each individual activity as separate line items, even though they are already included in the Multisport activity. Sometimes, the totals don't match because one or more of the individual items doesn't actually show up. For example, today I did intervals using Multisport. One of the individual items is missing as an individual activity, but it's included in the Multisport.
Activity Type Time
1 Other 7:17
2 Running 9:46
3 Multi-Sport 30:28:00
In the example above, I walked for about 13 minutes, ran for 7 minutes (7:17), and walked for around 10 minutes (9:46). 13+7+10 = 30 minute total seen in Multisport Row 3. The individual activities, Rows 1 + 2 should equal 3, but there's an "Other" item missing (unless I open the Multisport activity and look for it separately). And, when exported, the Multisport activity becomes duplicate information--doubling my time, miles, and calories for the day.
Then, in the Calories In/Out tab in Garmin Connect, all of the above are totaled. So, my total calories burned today is double what I actually burned. The detail shows the calorie total for each individual activity (except the missing one) plus the Multisport total. Instead of the correct value of 189 calories, it's 79 + 29.
I did another Multisport in the evening, and instead of the 319 calories burned which was the total of all the activities, in the Calories In/Out feature, it shows double that amount for the workout.