This will occur if the selection package on the selected benefit from the previous category selection package on the account is null.

When you have a category selection package benefit in batch detail, you should select it and hit F9 to bring up the list of benefits to choose from and select from there. That populates the selection package on the resulting benefit, for reference in defaulting later.

However, if instead of doing F9 you just change the category selection package benefit in batch detail to the name of the specific item you want, the selection package will NOT be stamped on the benefit, and thus defaulting to it will not be possible.