I have found two different brands that offer a set of stain/dyes in alcohol, oil and water, and a set of clear tops like alkyd varnish, lacquer, polyurethane, etc.
Both says in the fine print, that their oil based dyes, are not recommended to use prior a polyurethane finish.
Lacking of further explanation from these both manufaturers in either their bottles or their websites, I wonder... why could an oil based stain be not compatible with polyurethane? what could happen if I do it?
I've been using the minwax formula oil based stain+polyurethane in several projects and worked great.
Additionally, if I keep on use this dye, then... just for the sake of avoiding an "unknown problem", could I use that zinsser sand sealer that's promoted as over-all, under-all compatible as an intermediate layer?