Hi Scott by "memory" I think you mean that the pitch will soften when an area of the wood reaches the highest previous temperature that it was previously exposed too - is that correct?Pine pitch has a "memory" and will usually harden at 15 degrees less than the highest temperature that it has been exposed to. Typically the pitch is set in pine at the end of a kiln run at 160F or higher.
Dave, it sounds as if your boards were milled from a longleaf or slash pine tree. Sometimes SYP can be a real bear to accept a stain. You will most likely have the best results if you don't stain it. As Jeff recommended, an initial coat of shellac should work well.
If so, that explains why air died or unset pine pitch will soften when machined. Machining (jointing, planing, sawing, routing, sanding) does create some heat on the area of the board machined, which would result in pitch softening. At least that my experiences with pine in general.
If this is the case then the OP may be in good shape as long as the finished piece does not get to a temperature higher than what the lumber was previously exposed to <--- seeking your wisdom here.