for 苏盈盈 遇 Tan and not 黄杨策 could be due to the remaining 6 players are unable to form 3 pairs due to the previous rounds played. Usually the software will break the latest pair formed and redo the pairing again. For this reason, the pair of 陈茗芳 and 洪黛欢 will break and redo again if the remaining 8 players could not form 4 pairs.
I believe the same set of parameters are used for Groups A & B too.
As for why not using Round Robin System for ladies this year, the possible reason could be the number of lady players for the past few years was 8 or less, up to 7 round round-robin system is enough, may be SIXGA EXCO could cover the review of this point for 2009 Ladies Open too.