It leaves so much unknown. You think jump to game is the safe and weaker option but no
I appreciate hearts is fairly safe game but what is wrong with diamonds?
How do you know you can go for hearts or No trumps in general with that bid?
It says invite but to what - I assumed diamonds
Those who tried blackwood discovered that North assumed it was diamonds
EDIT I ran it through a practice table and the South bot passed. Strange that I and every other table in my section saw a heart or diamond game. If you bid 4D it gets passed out. You can see my problem now Some tables even saw possible slams and tried to stop too late. One table really impressed me by passing the 5H response to Blackwood. Final note, no matter how hard I try I cannot get to 5 diamonds despite the invite except briefly in passing as you can see.