Expand columns after query merge is updating the column values

Hi , I am trying to merge two tables based on ID column. After merge i am expanding the table to get two date columns D1 and D2, which are also there in two tables that i am merging. But after expanding value of the D2 column in first table is getting updated.

I tried different ways but unable to find out why the value is getting updated during merge.Its Date/Time type column.

Thanks,

Vijay.