I ran a test to elucidate the 'six-second' problem: 3C454.3 (35
Jy), switching bands every minute, but with 1-second averaging, rather
than 3-second averaging.
The 'non-closing' phase seen in the last two scans of the 3-second
averaged data is now in the last two scans of the 1-second averaged data.
A CBE issue ?