DW-Q520A with HFS2 -- what is the beast?



Just got a slimline Sony DW-Q520A (LiteOn) with firmware HFS2 (24 Apr 2006). Looks a bit odd – for what I know, the “usual” f/w for this drive is HYS1 and HYS2. Anybody knows what the HFS2 beast is?
Comparing media code table with HYS1 (published elsewhere), there is one new record, 298 in total.
According to CD-DVD_Speed, bitsetting is supported for DVD+R and +RW, but not for +R DL. Is it the same with HYS1 and HYS2?
Another oddity is that, although there are two LED’s, only one (orange) is used in any mode of operation.