Can someone explain this Sent thread sorting?

People,

I attach a screen capture of my RoundCubeMail Sent box - why does the second item on the list, which is a separate reply to the thread above it, get sorted to position 2? By the date, and being a single mail, it should be much further down the screen . . I presume it is because the Subject is the same?

Thanks,

Phil.

-- Philip Rhoades

GPO Box 3411 Sydney NSW 2001 Australia E-mail: phil@pricom.com.au