Your Polar watch most likely has automatic lap splits enabled in addition to your manually recorded splits. In Polar Flow these will display in two separate columns as "Manual Splits" and "Automatic Splits". In Powercenter, only one "Distance Splits" metric exists. This means that a Polar watch with automatic splits enabled for every 1000m with manual splits at 400m and 800m will display in Powercenter as:
Polar Flow View:
Automatic Lap View:
If you are intending to use manual splits for a workout of varying distances, you will want to disable automatic splits in the Polar watch. You will need to do this for each individual activity in your Polar watch that you intend to use manual splits for.
For additional information, please contact firstname.lastname@example.org.