Well, the 8259 is the Programmable Interrupt Controller. Unless you are having a hardware problem, from say heat, my guess is that there is some screw-up in how the hardware configuration is understood and set up by the system.

A spurious interrupt, to me, would mean that it was unexpected in the sense that the device that is thought to have interrupted did not in fact have an operation initiated by the system. In other words, the device is thought to have said "I'm done!" when it hadn't been asked to do anything. This could happen if the interrupt request (i.e. IRQ 7 in your case) is shared between two devices and the interrupt handler after checking the first device, which was idle, does not know to check with the next device's interrupt handler.

Can you do: KDE Control Center | Information | Interrupts

to see how things are assigned?