Infiniti2000 said:
I missed it, since it wasn't directed at me, but I'll respond.
A close analogy, but not good enough. It fails when you realize that "spiked chain" is a specific weapon, and "flurry of blows" is not. Flurry of blows is a special attack, spiked chain is not. Flurry of blows requires a full attack action, a spiked chain does not. Therefore, this is a straw man.
Allow me to play devil's advocate for a moment. Let's assume that the spiked chain is being wielded by a 6th level fighter, who wants to get iterative attacks with it. This must be performed as part of a full attack action. In order for the monk to use a flurry of blows, it must be part of a full attack action as well.
The description of each rule is framed as "When using [the ability or weapon], [description of consequences]. If we take "when using" to imply "if you use it, you are considered to be using it for the duration of the full attack action", it seems as though there are a particular set of consequences:
Using a flurry of blows during the full attack action prohibits using secondary attacks that are not also special monk weapons, and using a spiked chain during the full attack action grants a +2 bonus to disarm checks. However, once the fighter has used the spiked chain, he is considered to be using it for the remainder of the full attack action, no matter what else he does. He makes one attack with the chain, then lets go with one hand, pulls a dagger, and attempts to disarm with it. Since he is still considered to be using the chain, he satisfies the conditions required to gain the +2 to the disarm attempt. Even if he drops the chain entirely, he should still gain the bonus.
If we take "when using" to imply "when making rolls directly related to the ability or weapon in question", we get a different set of consequences:
In his dagger attack, the fighter does not gain the bonus because he is not making a roll to disarm with the chain. However, that changes the monk's options. As part of a full attack action, he rolls for his flurry of blows attacks. Then, he makes an off-hand attack. Since this action is not directly related to the flurry of blows, it need not be made with a special monk weapon. Since a flurry is made as part of a full attack action, but is not necessarily the entire full attack action since other things may also be part of a full attack action and the flurry of blows description does not explicitly prohibit these things also being used, the weapon requirements are only applied to those rolls which are made "as part of a flurry of blows".
I think that the issue here, and the issue with Iku's other example, is that there are two interpretations of the words "when using". Under one interpretation, "using" is a state that lasts for the duration of the full attack action, and under the other it's not. But in the former case, we run into the spiked chain disarm problem, and in the latter, monks can use longswords as off-had attacks. Of course, the latter is only a problem if the rules prevent it, but the former just doesn't make any sense. Still, that might not be a good enough reason to go with one interpretation over the other.
So I think the problem is that the words "when using" are poorly defined, and this leads to multiple incommensurable interpretations.