F.8912 is supported by MeF but apparently not by Intuit.

Since it's a tax form that requires IRS processing, unless PS has a link under e-filing attachment to F.8912 (there isn't in Lacerte/ProConnect), it shouldn't be uploaded because it won't be processed.  You should see a warning in PS similar to what's in Lacerte/ProConnect:

• NOTE: Do not attach any document that needs IRS approval or attention

Instead, F.8948 should be sent with the paper-filed return and the following box should be checked with the blanks filled in:

• 5. The preparer’s e-file software package does not support Form ____________ or Schedule ___________ attached to this return.