"The problem is turning mental being into real being. Because scientists use concepts that exist in mind but can't have independent existence in reality they start to attribute real existence to these mental entities."
---Aquinas3000 over at Edward Feser's blog.
But it's no problem if you're not assuming that the mental can arbitrate that initial difference between "mental" and "real" to begin with in the analysis itself.
Also, why should mind objects need to exist beyond the factors they are in thought? In fact, that is even more real than the unstable "reality", since mind objects adjudicate and pass constant judgment on what is "real" and what is mental just to use them as distinct terms in the discussion.
I don't know how anyone could decide what is "independent" existence in "reality" without criteria that is itself already independently existing as a necessary operating system of evaluative thought that we necessarily use universally in analysis.