Note: This is question to which I have already found an answer. It seems that posting a question after finding an interesting answer is encouraged, so I am posting this. Someone else is likely to have the same problem and find this useful.
I have an iOS app that produces charts. Shortly after publishing an update, a user sent me this panicky email:
"the latest update has modified the curves ... not seen more growth curves and inserted data are represented as a line descending ... before you could see perfectly well
Help me"
I get him to send a screenshot and give more detail. He has an iPhone 3G and this is how girl's chart looks. Most points are drawn at the wrong coordinates: they appear to be drawn at (x,x) instead of (x,y).
Compare with how this is supposed to look (ignore the difference in colours -- pink is for girls, blue for boys):
After much experimentation, I send him a rebuilt version of the previous version (which worked OK for him) and it still doesn't work. So in the end it appears that the code changes in the update have nothing to do with it. What could be the explanation?