With apache 2.3.15 I had kinda the same issue with mod_fcgidon ubuntu 8.04 as on windows. With -k restart or -k graceful the server did not die like on windows, but the server delivered than only a 200 OK response header, but nothing more. Switching from worker mpm to event mpm seemed to solve this, but the server died later :-/
Since it has talmost the same issues like on windows I could make a patch that fixes this. Grab the patch (patched against trunk) for the patch for 2.3.6
The bug 50309 is now longer than a year listet. Bad that none applied it yet.