  We revisit qubit-qutrit quantum systems under collective dephasing and answer
some of the questions which have not been asked and addressed so far in the
literature. In particular, we examine the possibilities of non-trivial
phenomena of {\it time-invariant} entanglement and {\it freezing} dynamics of
entanglement for this dimension of Hilbert space. Interestingly, we find that
for qubit-qutrit systems both of these peculiar features coexist, that is, we
observe not only time-invariant entanglement for certain quantum states but we
find also find evidence that many quantum states freeze their entanglement
after decaying for some time. To our knowledge, the existance of both these
phenomena for one dimension of Hilbert space is not found so far. All previous
studies suggest that if there is freezing dynamics of entanglement, then there
is no time-invariant entanglement and vice versa. In addition, we study local
quantum uncertainity and other correlations for certain families of states and
discuss the interesting dynamics. Our study is an extension of similar studies
for qubit-qubit systems, qubit-qutrit, and multipartite quantum systems.
