There's still chatter about how the Pakistani ISI might have had something to do with the Mumbai massacre, especially on the center-right (the left flat-out doesn't care). The ISI would be stupid to do it though, and while that's not impossible, there are too many reasons why it would behoove Pakistan to disallow it if possible.
First, there's no strategic logic to the ISI involving themselves or allowing the Mumbai attack. There's been a solid cease-fire over Kashmir since 2004 and in some places, there's discussion over demilitarizing completely. The only reason that could support the kind of covert action seen in Mumbai would be if diplomatic proceedings had gone dramatically wrong for Pakistan, and they thought it necessary to force their hand to get back into a position of strength in the negociations. To people who follow Indian politics (all three of you), it's clear that this didn't happen, at least not overtly. Public tensions were about normal in the weeks leading up to the attack, so there's really no suggestion that the relationship had gone sour. It's not impossible, just very unlikely.
Second, it's important to remember that while the ISI may have had a significant hand in the formation of Laskshar e-Taiba as an anti-soviet proxy, that this group wasn't formed out of thin air. There was a group of people there before willing to fight or close to that mark, and they were co-opted by the ISI. That's the only way a viable insurgent group starts; without pre-existing internal volition, insurgencies don't start or last, and can only be supported temporarily by covert funding and influence. What this means is that the relationship between the ISI and Lakshar e-Taiba is not characterized by the heirarchal notions suggested by a creator-creation relationship. It's symbiotic; both feed off eachother, but do not neccesarily operate to eachother's benefit and it is defined more by influence than control. Lakshar e-Taiba will have its own agenda and modus operandi, and it will not always be to the ISI's benefit, even if they cooperate where it suits them. Other examples will include the relationship between the CIA and Nicaraguan Contras, and the relationship between the US Military and the 1920's Brigade in Iraq.
And, just like the 1920's Brigade does things that the US Military doesn't always approve of, just like the Contras sometimes resorted to human rights abuses that were detrimental to the CIA's cause, Lakshar e-Taiba will occasionally act without regard for the interest of their co-opter.
It's important to understand that Lakshar e-Taiba is not a "Pakistani" group per se; it's fallacious to label them as such because they're really a transnational terrorist group that happens to operate out of Pakistan. Their interests are Islamist interests, not Pakistani interests, and there's going to be a pretty wide gulf between them on a regular basis. The influences of their base nation take a side seat to the interests of their religious convictions wherever those interests end up in competition. The Mumbai assault is a very good example.
The attackers did throw out some pretty generic stuff about Kashmir, but it was oriented towards the percieved crimes against muslims and Islam in Kashmir, making the assault not a nationalist issue over Kashmir, but a religious issue. This is perhaps what makes it a little confusing when considering whether or not it was really about Kashmir. It was, but in a different context than is normal. Further, the attackers made clear that they percieved Kashmir as land belonging to Islam; to them, the attempted ceding of the territory to China by Pakistan in 1964 is just as illegitimate as the Indian claim to the territory; they're both tahut, just to different degrees.
The result was an islamic attack on India over Kashmir in Mumbai, which was against Pakistani state interests and only has a valid strategic logic when understood in an Islamist context. But it would be short-sighted to leave the blame with nobody but these Islamist groups, because they are so often co-opted by nations as proxy utilities against conventional military and political power. There must be some reasonable amount of responsibility levied on the people and institutions who continue to co-opt these groups, and lend them legitimacy in doing so. The ISI here is only distally responsible, and probably not responsible at all for the Mumbai assault - that one belongs entirely to Islamism (and if the ISI participated, they were profoundly stupid for doing so). But it's also clear that the relationship, however strained now, can't be allowed to continue if halting preventable terrorism is the interest.