Given that Haste, Rapid Shot, and Flurry of Blows, for example, all use essentially identical wording:
When making a full attack action, a hasted creature may make one extra attack with any weapon he is holding.
You can get one extra attack per round with a ranged weapon. You must use the full attack action to use this feat.
When unarmored, a monk may strike with a flurry of blows at the expense of accuracy. When doing so, she may make one extra attack in a round at her highest base attack bonus, but this attack takes a –2 penalty, as does each other attack made that round. A monk must use a full attack action to strike with a flurry of blows.
... it would seem to me that if one disallows Flurry and TWF (due to "You must use a full attack action"), one must also disallow Haste and TWF, or Rapid Shot and TWF.
But none of those appear supported by the rules, to me - it's not like Circle Kick or Dirty Fighting, which stated "When taking the Full Attack Action, you can
give up your regular attacks, and..."
As far as the most recent WotC comment on Flurry and TWF, Andrew Finch (RPG R&D Development Manager, WotC) addressed it in
this thread, stating "Sure, no problem"...
even for a monk striking unarmed.
I disagree personally with that last, but I certainly agree that in 3.5, it's possible while using special monk weapons.
Interestingly, in 3E, it
was possible to combine TWF and Flurry, with a single monk weapon in your primary hand.
A monk fighting with a one-handed weapon can make an unarmed strike as an off-hand attack, but she suffers the standard penalties for two-weapon fighting. Likewise, a monk with a weapon (other than a special monk weapon) in her off hand gets an extra attack with that weapon but suffers the usual penalties for two-weapon fighting and can't strike with a flurry of blows.
You're fighting with a one-handed weapon, so you can explicitly make an unarmed strike as an off-hand attack (suffering the standard TWF penalties).
You don't have a weapon in your off-hand, nor are you using any weapon prohibited in a Flurry, so you're not prevented from striking with a Flurry of Blows.
-Hyp.