Lookup Field Issues

I have a lookup field in a table that is "text" data type and
restricted to values in the list. It works properly when entering
data, meaning it won't let the enterer remove the focus from the field
if the text they've entered isn't in the list. But for some reason it
will allow text values to be pasted into the field even if they aren't
in the list. I want to use the field to check for consistency in
preexisting data using copy and paste. In my experience this should
create a "Paste Errors" table with all the records having a value for
this field isn't in the lookup list. Any ideas why I'm not getting
paste errors in this case?