This is on par with how Java WebStart locale reporting works between Windows and Linux.
AFAIR, Windows always reports US_EN for the locale, so you can write locale unaware code everywhere, but when running on Linux, you get the correct locale of the system (of course), and things break spectacularly.
I remember debugging an integer overflow, and I literally facepalmed following a "you didn't do THAT, did you!?".
The thing they did was parsing the date from the date string (formatted for system locale, without giving a specific locale) Java returned to them instead of fixing the locale and getting the date or getting the parts with relevant functions.
I have a relatively short fuse for people who doesn't read (or at least skim) the manual of the library they're using.