  We report on the detection of very stable modulations with periods
unexpectedly (~0.5%) longer than superhump periods during the slowly fading
stage of WZ Sge-type superoutbursts in three systems, GW Lib, V455 And and WZ
Sge. These periods are naturally explained by assuming that these modulations
are superhumps arising from matter near the tidal truncation radius. This
finding provides an additional support to the hypothetical idea of expansion of
the accretion disk well beyond the 3:1 orbital resonance in some low mass-ratio
systems. Combined with the effect of 2:1 resonance, we present an explanation
of the origin of positive period derivatives in certain short-period SU
UMa-type dwarf novae.
