  We will study commuting properties of the defect functor
$\mathrm{Dev}_\beta=\mathrm{Coker}\mathrm{Hom}_\mathcal{C}(\beta,-)$ associate
to a homomorphism $\beta$ in a finitely presented category. As an application,
we characterize objects $M$ such that $\mathrm{Ext}^1_\mathcal{C}(M,-)$
commutes with direct unions (i.e. direct limits of monomorphisms), assuming
that $\mathcal{C}$ has a generator which is a direct sum of finitely presented
projective objects.
