  We build on our detailed analysis of time-series observations of the globular
cluster M 68 to investigate the irregular pulsational behaviour of four of the
RR Lyrae stars in this cluster. M 68 is one of only two globular clusters in
which mode-switching of RR Lyrae stars has previously been reported, and we
discuss one additional case, as well as a case of irregular behaviour, and we
briefly revisit the two previously reported cases with a homogeneous analysis.
We find that in 2013, V45 was pulsating in the first-overtone mode only,
despite being previously reported as a double-mode (fundamental and first
overtone) pulsator in 1994, and that the amplitude of the fundamental mode in
V7 is increasing with time. We also suggest that V21 might not have switched
pulsation modes as previously reported, although the first overtone seems to be
becoming less dominant. Finally, our analysis of available archival data
confirms that V33 lost a pulsation mode between 1950 and 1986.
