  The red clump stars in the open cluster NGC 752 present a peculiar
distribution in the colour-magnitude diagran (CMD): the clump is observed to
present a faint extension, slightly to the blue of the main concentration of
clump stars. We point out that a similar structure is present in the CMD of NGC
7789, and discuss their possible origins. This feature may be understood as the
result of having, at the same time, stars of low-mass which undergo the
helium-flash, and those just massive enough for avoiding it. The ages of both
clusters are compatible with this interpretation. Similar features can be
produced in theoretical models which assume a non-negligible mass spread for
clump stars, of about 0.2 Mo. However, one can probably exclude that the
observed effect is due to the natural mass range of core helium burning stars
found in single isochrones, although present models do not present the level of
detail necessary to completely explore this possibility. Also the possibility
of a large age spread among cluster stars can be refuted on observational
grounds. We then suggest a few alternatives. This spread may be resulting
either from star-to-star variations in the mass-loss rates during the RGB
phase. Alternatively, effects sush as stellar rotation or convective core
overshooting, could be causing a significant spread in the core mass at
He-ignition for star of similar mass. Finally, we point out that similar
effects could also help to understand the distribution of clump stars in the
CMDs of the clusters NGC 2660 and NGC 2204.
