This problem is addressed in ArcGIS 8.1 Service Pack 1. See the Related Information section to download this pack.
This problem occurs when editing data from a geodatabase where there are subtypes defined.
When changing a subtype for a row using the Attributes dialog box, defaults defined in the subtype are applied. If you use the table window to change the subtype, the defaults are not applied.
If possible, use the Attributes dialog box to change the subtype. Otherwise, the appropriate defaults will not be applied.