[Mp4-tech][video] modulo time question

[Sandip Parikh]

Hello:
I recently came across a MPEG-4 (SP L1) stream that did not always have
modulo_time_base set to non-zero when the vop_time_increment wrapped
around:
vop_time_increment      modulo_time
340                                    0
407                                    0
474                                    0
541                                    0
0                                        0    // modulo_time_base
remains 0
67                                    0
134                                    0
201                                    0
Is this valid ? If so, how should a decoder interpret the presentation
times ?
Thank you,
Regards,
Sandip