Partner (shockingly!) leads your suit with the 3 of ♥ - you win the Ace and declarer follows with the 4. We do not lead low against NT without an honor so we can mark partner with the K or J or both.
Like a good little student, I you return your original 4th best - the 5 (just as every bridge book you have ever read has told you to do.) Declarer plays the 9 and partner wins the Jack. Partner proceeds to go into the tank. Clearly he has KJ83 and thinks you started with A52. He is hesitant to cash the K and lose tempo while setting up a trick for declarer. Eventually he decides to switch.
Is there any solution to this? Would leading the 2 be the correct play? Are we now fooling partner that Hearts are 4-4? Might he now inadvertantly block the suit if he thinks he wants to be on lead at trick 5?
*****
One other note .. upon retrospect I think the Q at trick one is the correct play (catering to partner leading from Jxx). But this doesn't change the trick 2 issue at all .. when I lead back the 5 (declarer playing the 9) and partner winning the J, won't he now be playing declarer for A109x and abandon the suit? The 5 leads to the same ambiguity.
Is the expert rule still "original 4th best" or is there any better way to deal with this? All of my bridge books are 20+ years old lol please tell me someone has come up with something better!