It may be operating correctly. According to the Tek 468 operator's manual, page 18, "Source Switch:" "The waveform displayed on the CRT is the source of a composite trigger signal. Stable triggering of non-time related signals usually can be obtained by setting VERT MODE to ALT, SOURCE to NORM, COUPLING to LF REJ (high frequency signals only) and adjusting thru Trigger LEVEL control for a stable display. Time relationship between the Channel 1 signal and Channel 2 signal is not indicated on the display."
A case of only having one trigger level for two sources. LF REJ or AC Coupling removes any DC bias between the Channel 1 and Channel 2 signals, allowing a single trigger level to be used for non-overlapping signals. "A trap for the younger players, there."
I believe the Tek 465B is similar, although I could not find a similar reference in the Tek 465B manual.
VR,
Kevin