Our previous pull switch in the bathroom was wired in a similar way with only three single reds the difference being two Reds were connected to COM and the remaining red to L1 which turned out to be the switched live to the light. This method of wiring was consistent with all the other light switches. The live loop in was done at the switches rather than in the rosettes, neutral was provided by a single which simply went from light fitting to light fitting.

In my opinion I feel your switch has been taken off at sometime and replaced incorrectly, check some of the other light switches it may be that your lighting circuit has been wired similar to mine.

Richard