Oil based stain incompatible with polyurethane?

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.
Any idea?

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?

My primary buisness is furniture repair. I probably see between 200 and 400 pieces a year in the shop. Every year I see several pieces that have poly over something else, what appears to happen is the film of poly seperates from the surface wherever it is scraped or scratched, it doesn't come off but forms sort of a bubble. The film is in tact but seperated from the surface. Poly is not repairable nothing will stick to it so the only choice is to strip the piece and refinish. I have seen this on old refinished pieces and on newer pieces where poly was the original topcoat. You may be able to tell I am not fond of polyurethane varnish, I would use alkyd or lacquer.

Thanks a lot for your opinion.

Now, about the furniture you talk with polyurethane falling apart... why do you think that happen?
Were they old furniture?

I have seen this on older and newer pieces. I believe that poly has adhesion problems when applied over some stains and sealers or other finishes.

Tom & Cesar,

Poly varnish is notorious for being tough, but it's not hard. AND it has poor adhesion qualities which is WHY you MUST sand between coats. If you don't sand it can easily delaminate.

Adding poly on top of an oil stain is asking poly to stick to something that it doesn't like to stick to in the first place... poly doesn't even stick to poly very well.

FYI - Shellac will stick to just about anything... even teflon. Yes it is a great barrier oat however if you use shellac make sure it's DE-WAXED shellac or the poly peel off with no trouble what so ever.

Thanks a lot to both for your comments.

Maybe to make this discussion shorter I have to ask more directly:
Why the minwax oil-based system recommends to Polyurethane over Oil based stains?
Do they change their formulas to assure compatibility?

Because they sell a lot of one part polyurethane over the counter.

Generally the faster you get away from home center polyurethane the happier you will be.

I imagine that minwax formulates all their products to operate together and you could use their poly over their stains after a suitable drying period. With all the quality finishes available I don't see a reason to use it anymore.

Joe

I've used Minwax poly over minwax stains and have never had a problem. I imagine the varnish binder content in the stains is either so small or is urethane-based to insure compatibility.

The stained surface also probably has enough 'scuff' that mechanically it provides decent bite for the polyurethane.