Punching the air with a transformed tome does not change the tome back.

I'll check that. Can you tell me which book the tome was when you tried this?

I'm also experiencing this issue. For me, it appears that all books are affected, but a specific tested example would be the guide book from Modern Industrialization.

I'm running the game with many other mods installed; here is a complete modlist: https://gist.github.com/unilock/bffcfe138d617f1a187d76f93278e2b4
It's likely this is a mod conflict of some sort.

Unfortunately, there doesn't appear to be any helpful information in the logs regarding this issue.

My slightly hacky fix was to add a listener to InputEvent.InteractionKeyMappingTriggered that calls MorphingHandler#onPlayerLeftClick if the conditions are met for an "empty left click":

NeoForge.EVENT_BUS.addListener(InputEvent.InteractionKeyMappingTriggered.class, event -> {
    if (event.isAttack() && Minecraft.getInstance().hitResult != null && Minecraft.getInstance().hitResult.getType() == HitResult.Type.MISS) {
        MorphingHandler.INSTANCE.onPlayerLeftClick(new PlayerInteractEvent.LeftClickEmpty(Minecraft.getInstance().player));
    }
});

I guess some other mod is cancelling either this event, or PlayerInteractEvent.LeftClickEmpty.

Could be the case yep. Gonna investigate further