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A possible explanation. The bandwidth of these machines is just about wide enough to record the entire composite colour signal. Assuming the E-E route goes via the FM mod/demod (often true for machines of that period) this suggests the bandwidth is indeed wide enough. The problem on replay is inherent mechanical instability taking the subcarrier frequency outside the locking range of a monitor.
This was also true of quadruplex VTRs where the highly complex "Colortec" timing corrector was designed to overcome the problem. A very few external timebase correctors could do the necessary correction for helical scan VTRs. I have seen similar effects with PAL colour on the highband version of the Ampex VR7003. This too was specified for colour but I didn't have the colour timing correction board for it nor a suitable TBC.
Most helical scan VTRs used a "colour under" method where the chroma information was separated and recorded as an AM signal at a much lower frequency. The replay processing included circuitry that heterodyned the colour back on to a stable subcarrier.
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