  We study the dependence of fragmentation in massive gas-rich galaxy disks at
$z > 1$ on feedback model and hydrodynamical method, employing the GASOLINE2
SPH code and the lagrangian mesh-less code GIZMO in finite mass mode. We
compare non-cosmological galaxy disk runs with standard blastwave supernovae
(SN)feedback, which introduces delayed cooling in order to drive winds, and
runs with the new superbubble SN feedback, which produces winds naturally by
modelling the detailed physics of SN-driven bubbles and leads to efficient
self-regulation of star formation. We find that, with blastwave feedback,
massive star forming clumps form in comparable number and with very similar
masses in GASOLINE2 and GIZMO. The typical masses are in the range $10^7-10^8
M_{\odot}$, lower than in most previous works, while giant clumps with masses
above $10^9 M_{\odot}$ are exceedingly rare. With superbubble feedback,
instead, massive bound star forming clumps do not form because galaxies never
undergo a phase of violent disk instability. Only sporadic, unbound star
forming overdensities lasting only a few tens of Myr can arise that are
triggered by perturbations of massive satellite companions. We conclude that
there is a severe tension between explaining massive star forming clumps
observed at $z > 1$ primarily as the result of disk fragmentation driven by
gravitational instability and the prevailing view of feedback-regulated galaxy
formation. The link between disk stability and star formation efficiency should
thus be regarded as a key testing ground for galaxy formation theory.
