When I choose doubles for whatever the task is (say computing pretty fractals), I expect the full precision of the underlying apparatus. Granted, stringification is not very expedient in this case, and hence, even the more cause for nasty surprises.

As for what are the odds that truncation accidentally leads to correct result? Sorry but no, hell no, I do not need anybody guessing (poorly) what the result might have been. I just need the calculations done as programmed.

Edit. I'll add this little anecdote about astronomical odds.

Two friends are idly looking out the window; the street is all but empty save for occasional traveler passing. One says, "hey, I'll bet a penny for your watch that the next one hundred passers-by are all men!" His mathematically astute friend replies, "taken! You'd better have that coin ready, because the odds for that are, quite, a-stronomical!" Very soon after, the first person slyly remarks, "What do you think, isn't that a soldiers' marching song we hear approaching?"