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All sets with a vertical hold control suffered from this to some extent. The problem is due to the high-voltage, high-current horizontal sweep getting into the vertical sync. This is very hard to compensate in any given chassis, since it can be a function of ground loops from the horizontal sweep circuit, and once the chassis and circuits are laid out, trying to fix them could be impossible. Later chassis that used a digital countdown for sync fixed this once and for all, since it could trigger on the edge of a 2x horizontal frequency and therefore start vertical retrace exactly on a whole line or a half line on alternate fields.
In 1953, Motorola even based an ad campaign on the quality of its interlacing.
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