When a dimension is populated from two different sources, a phenomena known as Flip Flopping could occur. Source1 populates an attribute with Value1, whereas Source2 populates the same attribute with Value2. Everyday, the ETL creates a new row with the attribute = Value1. Then a few seconds later it closes that row and creates another new row with the attribute = Value2.
Today is 21/8/2015, current time: 7:35am. ProductKey 3156 is yesterday’s rows. The ETL this morning closed this row at 4:12:27. It then created a new row (3157) because it thought that the size of the tumble dryer was 7 kg (sourced from Source1). 4 seconds later, the ETL read Source2 and the size there was 6 kg. So it closed 3157 and created 3158 with size = 6 kg, which is now the active row.
To solve this, either update the source system to agree on the same size (best approach), or customise the ETL to ignore the size data from one of the two sources.