We have set uploaded the stemmers from the SDK Samples to WorldServer and they are now visible under
Management > Administration > Customization when selecting Word stemmers:

Setting values for
Configure Stemmers for Desired Languages in a term database under
Management > Linguistic Tools Setup works fine:

We then open the term database options again, remove the
Configure Stemmers for Desired Languages entries, and click
Save:

But opening the term database settings one more time shows that the changes have not been saved:

And the
Configure Stemmers for Desired Languages settings remain in the
dbo.tdDatabaseStemmers table.