Cyberyeti, on 2016-August-11, 14:21, said:
So partner forgets your relay, fails to alert and bids 4♥. You haven't guaranteed more than 4 hearts by relaying, just that you're inv+ and he can bid a GF 3♥ over 2♥ with a maximum and 2N with a minimum with 3 hearts, clearly he doesn't have 4 or doesn't bid 2♦ so 4♥ seriously doesn't exist.
In a context where partner had alerted and explained the relay correctly, you would be sitting there trying to understand what random hands he would bid like this. I suspect you would think that his 2
♦ was the misbid rather than the 4
♥ and would pass, thinking partner has four small hearts, one more than he had when he bid 2
♦. The double could easily be based on four good trumps and the fact that both of you might be minimum.
In a context where partner did not alert the relay, your mindset is that 4
♥ is the misbid so it's very difficult to think about what to do without taking an enormous amount of time. This is why UI problems are so difficult at the table.