Thanks for reporting that. I see similar problems in a couple of other coreutils 
programs. The style elsewhere seems to be to try ftruncate first, and report an 
error if it fails only if the file is not one for which POSIX specifies the 
behavior, so I think it'd be better if 'split' did that too. So I installed the 
attached patch to fix the problems that I found, and this should fix the bug you 
reported so I'll close the bug report.

Thanks also for the test case. To install that I'll need a copyright assignment 
form signed; can you do that for us? If so, please let me know and I'll get the 
paperwork ball rolling for you.