My sleep data is wrong, depending on the start time

[igorman]

Sometimes I edit the start of my sleep time so I can see how napping effects my sleep during the night, and when I did that last night, I realized it actually changed the data reported in the middle of the night, which is wrong.

When I look at how I slept during the night from 10:12 - 5:26, I see this:

Notice how little REM sleep I had in the middle of the night.  Now when I look at the whole night to see how much I dozed off earlier in the night starting at 7:12, I see this:

Notice how there is now significantly more REM sleep in the middle of the night.  One of these must be wrong, right?  Why is it that when I change my start time to earlier from 10 pm to 7 pm, do I see more REM sleep between 11-4?

[Terpsucka]

I have seen this too.  I routinely trim "awake" time at the end... when I'm just lazing in bed or cuddling, I don't want to reflect either way in my sleep score.  Generally when I cut this time out it raises my sleep score, but occasionally it lowers it, even when I'm only removing awake time.  One day last week doing this resulted in an increase in my REM time of nearly an hour, and a decrease in my deep sleep, both in the middle of my asleep time, like what you saw.  I would be curious why trimming awake time at either end would have that kind of impact.