RGB LED tape configuration oddity.

This is a section of the basic RGB tape that has individual red, green and blue LEDs. I'd always just assumed that the whole length was in sections of nine LEDs 3 red, 3 green and 3 blue with matching resistors in each section.
Recently I was playing about with a section of the tape and reduced the voltage to dim it a bit. As the voltage went down it became obvious that there were sections of nine and sections of six LEDs alternating along the strip.
I can only guess that this is a result of using a standard manufacturing size (500mm) of strip section, and having to adjust the series multiples to fit within that length.