General :: Hex Values Converting Inconsistently?

I couldn't really decide where this should be posted, but this is the most general of the forums. Anyway, I've been playing a wargame on intruded.net in which some of the challenges require me to pass hexvalues into the programs as character values. All is well with this, and usually I would use the shell to pass it in, but most of these programs use the gets() method to get my input.

Here comes the problem... The other day I was using my desktop which runs slackware 64 13.1 to do these challenges. My method was to use "echo -e 'xefxbexadxde'" to print them to the shell's standard output and then highlight and copy the resulting values to paste to the program. This works just fine on slackware, but when I repeated the same processes on Ubuntu 64 10.04 (which runs on my laptop) the 'xde' always turns up to be 'x00'. Then I tried some other levels with similar responses, not all the hex values convert to the correct ASCII characters.