I am running into inconsistent and possibly incorrect external application parameters.

1. I start Phoner as extension 2482
2. I call 2414
3. External application parameters show: 2414 2414 "2414"

But when calling an internal extension after receiving an external call the application parameter shows the previous incoming caller id as the first parameter.

1. I start Phoner as extension 2428
2. I receive a call from 848xxxx
3. I end the call with 848xxxx
4. I call 2414
5. External application parameters show: 848xxxx@213.19x.xxx.xxx 2414 "2414"

My test application is test.cmd with this content:
@echo off&setlocal
echo %*

I would think %1 should show initiator of call and %2 the recipient.  If so both cases are showing incorrect value as %1 but in either case the 848xxxx number should definitely not be shown in the second example.  So this looks like a bug to me.

There is a difference for incoming calls and connected calls.
If you are just interested for incoming calls, just configure to call your application in the first edit field.