Thanks for responding.
If you are asking if I come to a complete stop before shifting into first, no. At very low speeds I shift into first while rolling but give the synchronizer time to seed up. If, for some reason, I decide to put it in first at a higher speed (10-15mph) I rev match (let out the clutch in neutral, rev the engine a little, push in the clutch and move the shifter to first). In either case, the shifter slides into first easily, without force or fuss.
We've been driving standard, between me and my wife, for a combined 92 years and haven't run into this before, except on a '46 Willy's that popped out of second every time you went down a hill in second, engine braking.
It takes very little change in speed to make it happen - like maybe 1 or 2 mph, always happens when decelerating or holding the car back with the engine, always at low RPMs and low speed.