I have written debug message to find the trigger is firing or not. It is going inside the block and displays the debug message of the block but it is not going inside the pre-update trigger.
kindly place this code in you custom pill and check what is event name.
Following events are only used is custom.pll .
We can't use pre-update.
SPECIALn (where n is a number between 1 and 45)
KEY–Fn (where n is a number between 1-8)
Refer below link.