Found a command variant (also in 6.1 and likely 6.0) that will crash the server so here's a new release...
In an attempt to rule out the memory allocator as the corruption problem I've set this version to use malloc/free instead of the ioFTPD internal memory allocator. I debug this way so it's got a lot of testing done using this configuration. Unless crashes become much more frequent and the internal allocator is helping to hide the error this will be the default from here on out...
Link:
ioFTPD-v6.2.1.zip
Code:
v6.2.1 Release Notes:
1) Fixed "site chown -R user[:group]" (where the directory/file/wildcard
isn't specified) to imply the current directory and all subdirectories,
and files instead of crashing with an unhandled exception.
2) Changed from the internal ioFTPD memory allocator over to malloc/free.