import with unique external ID overwrites

setup:

• create a dupe rule that matches on external ID only
• create a data file for import where the external ID for each row is unique, but the email address is the same
• import using the update option and selecting the external id dupe rule created

result:
each row is imported/updated to the same record. it appears to match on email, even though the dupe rule selected should only match on external ID

expected result:
since each row has a unique external ID, and that is our matching criteria, we would expect each row to be imported (not merged)

this only happens when importing with Update mode. if you import with the Skip mode, it correctly creates the records.

I've attached a sample import file.