  In the canonical understanding of transient X-ray sources the accretion
during quiescence occurs via a geometrically thin disk in the outer part and
via an advection-dominated hot coronal flow/ADAF in the inner part. The inner
part important for the radiation yields a hard spectrum. In most sources the
luminosity increase during outburst causes a change over to a soft spectrum
which can be understood as that of a multi-color black body disk reaching
inward to the marginally stable orbit. A few transient sources do not display
this transition to the soft state. We show that this can be understood as due
to relatively low peak luminosities in outburst in systems with short orbital
periods and therefore less mass accumulated in the then smaller accretion disk.
This is in agreement with the observations which show that most likely short
orbital period systems remain in the hard spectral state.
