mpegtsmux: pcr-interval, pat-interval, si-interval are not copied to underlying tsmux
When these properties are first set, mpegtsmux also sets them in tsmux (see gstbasetsmux.c, gst_base_ts_mux_set_property())
However, when a new instance of tsmux is created, they are not copied (see gst_base_ts_mux_default_create_ts_mux())
Adding these three lines to gst_base_ts_mux_default_create_ts_mux() solves the problem
tsmux_set_pcr_interval(tsmux, mux->pcr_interval);
tsmux_set_pat_interval(tsmux, mux->pat_interval);
tsmux_set_si_interval(tsmux, mux->si_interval);