Compose key problems

[thephotoman]

I'm a heavy user of the compose key, as I do work in multiple languages 
(Spanish and Latin are the most common).  The problem I'm having is that 
on the letters "a" and "o", the compose/hyphen/letter combination 
results in not a macron (as it should and does for the other vowels), 
but a tilde--a function also provided by the tilde key.

Is there any chance of getting this bug fixed, and is there a quick and 
dirty work around for it?