Reactive: root executed while updating a branch

[maximlt]

I was trying to understand what happens when a reactive expressions has multiple "reactive inputs".

graph TD;
    firstnamex-->append_lastname;
    lastnamex-->append_lastname;

Looking at the last cell of the image below, I'm surprised to see 'transforming first name johnny' being printed while updating lastnamex, is that expected?

from param import rx

firstnamex = rx('john')
lastnamex = rx('lenon')

def debug(value, info=''):
    print(info, value)
    return value

def append_lastname(fn, ln):
    return fn + ' ' + ln

pfnx = firstnamex.rx.pipe(debug, info='transforming first name').title()
plnx = lastnamex.rx.pipe(debug, info='transforming last name').title()
together = pfnx.rx.pipe(append_lastname, ln=plnx).rx.pipe(debug, info='merged')

together

firstnamex.rx.value = 'johnny'
lastnamex.rx.value = 'hallyday'