Hi and thanks for your post and question - it's a good one! Somehow, I noticed (after these few years), that there has been no comments or responses to your concern. I do have something to contribute now, if it's not too late.
As you may be aware, asthma can vary from patient to patient. Asthma affects everyone differently. Having said that, it is also true that folks have different responses to treatment and therapy. Some medications can cause a side effect which may cause a metallic taste for the patient. This naturally, does not affect everyone.
Were you ever able to determine what caused this for you?
Leon (site moderator asthma.net)