type checker plugin success depends on whether an expression is manually inlined

Hello list, The following file compiles with my plugin. It makes a data family HList have role representational in a way that I believe is safe: https://github.com/aavogt/HListPlugin/blob/master/ex/Coerce.hs#L19 I expect the highlighted line to be acceptable. However, it seems that the plugin never sees anything from line 19, when I uncomment it. Is there something I can do to make that L19 work? Is this a known or intentional limitation of type checker plugins? Thanks, Adam