  We compute the transcendental part of the normal function corresponding to
the Deligne class of a cycle in K_1 of a mirror family of quartic K3 surfaces.
The resulting multivalued function does not satisfy the hypergeometric
differential equation of the periods and we conclude that the cycle is
indecomposable for most points in the mirror family. The occurring inhomogenous
Picard-Fuchs equation are related to Painlev\'e VI type differential equations.
