Indeed. I tried it once in multiplayer, sharing the defensive while the target nation already had offensive. We wanted to test if a deactivated tech was permanent, or could be circumvented through tech sharing.
The share seemed to do the job, ie. 7 days wait for another diplomat and DI reduction, but the target nation didn't receive the tech (which is correct, of course

), and it showed up again in the sharable tech list. So, now I have to remember not to click that tech, or another week + DI is wasted.
If we are on this subject, I think that indeed tech that has been deactivated in the target nation shouldn't pop up in the list of sharable tech.
Furthermore, it should at least be an option to
NOT receive any tech shared to you by someone else, that will decativate some other tech in my tech trees. To stick with this example, if I haven't got defensive nor offensive doctrtine, I would want to keep the choice of which one I want activated, and not have my choice railroaded by an ally sharing the wrong one to me. Between humans, we have the option of negotiating and thus preventing sharing unwanted tech, but I cannot negotiate with the AI.
This, of course, applies to the panzer research tree far more than the doctrine tree. I don't mind that others share the building block tech for new panzer models to me (including the various tank gun sizes), but I would be rather upset if someone shared the tank model with a different gun than the one I would prefer. An extreme example would be a medium tank with a MG, instead of a real gun.
Jan Peter