The Tripping Staff feat mentions the following:
"..."
"Special: If you are a magus with the staff magus archetype, you can use spellstrike on any trip combat maneuver you make with the staff."
My question is, if you're using the spellstrike ability, which allows you a free weapon attack instead of a touch attack, does it act as touch spells normally do? Normally, a held charge is discharged the next time you touch anything or anyone, does this mean the same for poking someone with your weapon? If so, wouldn't the spell discharge if you trip someone with your weapon anyways?
I would rule it as you use the CMD for the trip and if you do trip the spell goes off as per a normal spellstrike.
Normally, even with spellstrike, you have to touch the person with a held charge in your hand to get the contact necessary. Spellstrike doesn't mean you hold the charge in your weapon, you simply channel it with an attack. If that makes any sense.