I was just working on a MUF to create zombies, and thought I would try out a vehicle object; the kind built into the server. That's when I ran into the problem. The @oecho isn't prepended to the string sent to people inside the vehicle at all, not even the default one.
I've confirmed this on Windows using cygwin with version 2.0b8.11 and 2.0b8.25.
A little correction on this. Unless the text sent comes directly from an in-server notify_exclude, the vehicle fails to echo at all. If it does get the string in exactly the way it wants, it fails to prepend the oecho. Currently the only way to fix this is to use the two-object vehicles MUF can provide.
Frankly I'm getting tired of using MUF to clean up bugs. I'd rather be using it to make new features.