I designed a part, let's call it original.SLDPRT, and then used the Split function to split it into two fabrication-ready parts, left.SLDPRT and right.SLDPRT.  As part of the Split process I create an assembly of the two, left_and_right.SLDASM, and add holes for fasteners and such that mate the two parts together, including a lip/groove feature.  To create the lip/groove, I edited left.SLDPRT in the context of left_and_right.SLDASM (creating the lip), and the lip/groove process has me choose the mating part right.SLDPRT for the groove.  And voila, it works.

Now, say I want to come back and edit the lip/groove feature (e.g., to change the reveal from 0.5 mm to 1 mm).  I assume this is done by editing left.SLDPRT in the context of left_and_right.SLDASM, where it was created.  However, I get this error message:

Unable to retrieve the matching feature.  Possible reasons:

     The mating component of Lip/Groove feature is a lightweight component.

     The mating componenet or matching feature has been deleted.

I see that the rollback bar for right.SLDPRT is before the lip/groove feature.  Dragging the rollback bar down doesn't help, because when I try to edit the lip/groove feature in left.SLDPRT, it automatically rolls back the associated feature in right.SLDPRT.  What's more, the same thing happens if I try to edit the lip/groove of right.SLDPRT (again in the context of left_and_right.SLDASM); the rollback bar for left.SLDPRT is above the lip/groove feature.

So it seems like I'm at a Catch-22.  I can't edit left because right is rolled back, and I can't edit right because left is rolled back.  How do I edit this lip/groove feature?

[Note that one workaround is to close and reopen the SLDASM file.  Then I am allowed to edit.  So perhaps this is a bug in SW 2012?]