I've seen the individual segments on an eticket be different once it posted, but in the end, all added up properly. i.e. segment 1 +2 both show as 100 PQD, but in the end, segment 1 posts as 125 and 2 as 75. Aside from 1 ticket which was a single PQD off, but likely a rounding thing (though usually, they are the same or rounded up to the higher $).
THe only time I've seen a major difference was in IRROPS that involve a day-of flight change, and even then, a quick call has solved it. I've also flown on a UA ticket with a CX segment, and the amount on the eticket was the same as I ended up getting.