Debra and I had a conversation at http://moodle.org/mod/forum/discuss.php?d=55849
Debra had encountered this:
<i>I created a calculated question. The student answered 1.59, which was correct and the feedback indicated the correct answer was 1.59 but still scored the student 0/2 pts. I checked to make sure the student did not put in any extra spaces or syntax. I edited the question and sure enough 1.59 is listed as a correct answer.</i>

I was able to duplicate the problem successfully

I have discovered what is happening.

formula is 6.375/

are various values fore.g. 4

Since you had mentioned: correct answer should have '2' decimal figures, the dataset has calculated the answers only upto 2 decimal figures...thus 1.59 is one of the answers in the dataset

The bug is: when you fill in the answer while attempting the question, it is not limiting itself to 2 decimals.
so try filling the follwing answers:
1.59---> incorrect
1.593---> incorrect
1.5937---> incorrect
1.59375---> Correct

Surprise!! surprise!!

Want more surprise?
Here you go===> this behaviour does not change even if you change the setting of 2 decimals to 3 significant figures.

Therefore, the bug is=> the decimal/significant figure option is affecting only the dataset for wildcard replacement but fails to be applied when answers filled in are matched with possible answers.

To take it further
if you click on 'fill with correct', it fills 1.59 only (taking it from dataset)
but if you click 'submit' then, it says 'incorrect'.

HOWEVER

once i set the settings as shown below, the preview started accepting 1.59 as correct. this was once decimal was set to 5 and tolerance to 0.01