Rob, empathy uses enchant so you should try the same text in tomboy as it uses it too, I tried and I can reproduce this in empathy but works fine in tomboy so this is indeed an empathy bug and btw bug 545424 will be marked a duplicate of this bug because seems like empathy have problems with spell checking so once this bug is fixed that will also be fixed automagically (talked upstream).
Rob, empathy uses enchant so you should try the same text in tomboy as it uses it too, I tried and I can reproduce this in empathy but works fine in tomboy so this is indeed an empathy bug and btw bug 545424 will be marked a duplicate of this bug because seems like empathy have problems with spell checking so once this bug is fixed that will also be fixed automagically (talked upstream).