Why is the invoice distribution Expenditure Item Date not always the GL Date

We are on Oracle EBS 12.2.5 and have set the following profile:  PA: Default expenditure Item date for supplier cost

Site level = Transaction GL Date

SELECT fnd_profile.VALUE ('PA_AP_EI_DATE_DEFAULT') FROM DUAL;  result = INVGLDT

Payables associates are performing invoice matching to Purchase Order lines that have a project and task.  They are not entering or changing the expenditure item date during the matching process.

99% of the time the expenditure item date on the invoice line correctly defaults from the invoice GL Date (as defined by the profile above).  Most of the exceptions to this seem to match either the invoice accounting date or the expenditure item date from the purchase order distribution.