hmm, maybe post some specific code, but it should be fairly accurate.  You could maybe test by putting a bunch of ret's and see if the output code is all C9's otherwise you could put Calcsys on you calc and use the debugging feature to see if the code you convert on the computer and (I'm guessing you're not using a cable to send the program, so you are using "asmprgm" and such to write it) see if the compiled code looks like what's on the computer

Its a text editor like notepad, but designed toward programming coding.

Possibility: it could just be outputting the hex value of every character i mean, last time i used text wrangler, i dont remember there being a built in z80 compiler...