  The beta decays of $^{86}$Br and $^{91}$Rb have been studied using the total
absorption spectroscopy technique. The radioactive nuclei were produced at the
IGISOL facility in Jyv\"askyl\"a and further purified using the JYFLTRAP.
$^{86}$Br and $^{91}$Rb are considered to be major contributors to the decay
heat in reactors. In addition $^{91}$Rb was used as a normalization point in
direct measurements of mean gamma energies released in the beta decay of
fission products by Rudstam {\it et al.} assuming that this decay was well
known from high-resolution measurements. Our results show that both decays were
suffering from the {\it Pandemonium} effect and that the results of Rudstam
{\it et al.} should be renormalized. The relative impact of the studied decays
in the prediction of the decay heat and antineutrino spectrum from reactors has
been evaluated.
