If you’re going to steal Fight Club research data and not give any credit at least use the most up- to-date data:
Extra attacks
Windfury Totem
- Can proc other extra attacks but not itself
- Can only proc once in a chain of extra attack procs
- For more in-depth information about WF see this wiki entry
Sword Specialization
- Can proc other extra attacks but not itself
- Can only proc once in a chain of extra attack procs
Proc items (Ironfoe, Hand of Justice, etc.)
- Can proc themselves and other extra attacks
- Can proc multiple times in a chain of extra attack procs
Multiple extra attack procs off a single melee swing
- Will show up in the combat log as gaining multiple extra attacks but will only grant extra attack(s) from one source
Multiple extra attack procs off a single instant attack
- Will grant extra attack(s) from all sources
All extra attacks
- Can proc enchants (e.g. Crusader), talents (e.g. Flurry) and items (e.g. Vis’kag, Heroism)
- Reset your main hand swing timer when they proc from your off-hand (e.g Flurry Axe)
- On-next-swing attacks (e.g. Heroic Strike) that are queued while an extra attack proc occurs will be cast immediately
- Multi-target abilities such as Whirlwind or Cleave have a single chance to proc extra attack(s) per-cast (as opposed to a chance per-target hit) as long as the ability hits at least one target
As for the topic at hand; Sword Specialization is not bugged – the testing method is flawed and has an extremely small data set with a high margin of error.