I'm developing an OS, so this isn't an application. Suspect this isn't the right forum, but I don't see anything appropriate for low-level OS development / architecture questions.
For testing purposes, I've programmed the PIT to generate a single interrupt and what I'm seeing is that multiple LAPICs accept the interrupt and execute the programmed IDT handler... Seems for these systems, I should really be using clustering - flat mode doesn't seem to work.
You may ask additionally in https://communities.intel.com/community/tech/processors and describe the indifferent behavior (saying suspected bug) of this processor. Let's see if they would find you the right persons for the answer.
Programming APs is an interesting urban area, but I don't find a strong excuse to have the APs servicing interrupts when we already have windows and linux......