Why is 'hidden' Opportunity field still displayed as a Constraint in the Has Opportunity filter?

[Elliott_Lowe1]

We have several custom Opportunity fields that are no longer used and are preparing to delete them from SFDC, but I want to be sure that it won't cause a sync error..  So first I made the fields not visible to the Marketo Sync profile.  In Field Management, the field name now has "Hidden" appended to it, but the field is still displayed in the Opportunity Info folder, rather than the Hidden folder

Also hours later the field is still showing as a Constraint in the Has Opportunity filter and I can select it and enter an argument.

And when I do so, in Field Management, the smart campaign now is displayed in the Field Used By section for this field. 

Also shortly after making one if the custom Opportunity fields not visible to the Marketo Sync profile, I received a Salesforce Sync Error message for that field, but that field is not required in SFDC and none the other fields that were 'hidden' from the Marketo Sync profile produced this error

Anyone have experience with hiding custom Opportunity fields that can tell me if this is this expected behavior or if am I doing something wrong.

[Grégoire_Miche2]

Hi Elliott,

This is weird and you probably need the support to step in.

Have you tried to add a contact to and opportunity in SFDC and checked if this oppy shows in Marketo (meaning that the opportunity still syncs, despite the error message).

-Greg