When primary key is selected, nullable is greyed out

When primary key is checked, the nullable column checkbox is greyed out.

This is all well and good if the nullable column is blank, but if it is checked as well, it makes it difficult to resolve the inconsistency (one has to uncheck PK, uncheck N, then re-check PK).

Suggest that either nullable checkbox should *not* be greyed out if it is checked, or alternatively that any action to check the PK field should uncheck nullable.