A user has reported that the num_sort routine has changed behaviour between versions 2.4.5 and 2.5.0. She has a multiple choice question using numbers with units that uses num_sort to order the options in numerical order. Under 2.4.5, no errors were reported, but under 2.5.0, she gets "non-numeric argument" warnings. I have changed the questions to remove the warnings.
I could understand why the error has been thrown, but I also see the utility in having a numerical sort on strings so that "7.4 m/s" comes before "47 m/s" in a list (and it would mean that I don't have to fix old problems :) Was this a design choice or have problem authors not taken advantage of this feature?
I'm not aware of a design choice that would cause this-- but it could easily have come from changes in the underlying perl (which is getting better at flagging things that it used to handle silently in some arbitrary way). It might be the unintended consequence of some other change, but at the moment I don't have any candidates.
A good start to figuring this out would be to have a specific example or two of a problem posted either here, or perhaps uploading it to bugzilla would be better, and then point to the bugzilla entry from here.
That will give anyone with some free time and an interest a chance to take a look at this to see exactly what is happening.