Why are non-hyperlinks behaving like hyperlinks?

I have a number of cells each containing a formula like the following:

IF(<condition>,HYPERLINK(<some link>,<a label>),"n/a")

So those cells satisfying <condition> should contain <a label> and should be clickable (to get to <some link>). Those cells not satisfying <condition> should contain "n/a" and should not be clickable.

And in practice, both do contain <a label> or "n/a" according to <condition>, but BOTH types are clickable, regardless of <condition>.

Why is that, and how do I stop it happening?

thanks.