It is true always. To use the "Auto-seat at buy-in" feature, you've got to have tables already configured. Because you buy players into the tournament one at a time (or more than one at a time), the TD doesn't know how many players you will eventually have in the tournament. In order to properly balance players, the TD needs to know how many players you have and how many tables and seats you have. Without that knowledge, balanced tables can't be achieved.
Consider this: there are 2 things that can be done in order to randomly seat players as they buy-in.
1) Begin filling up one table at a time. When you fill up a table, move to 2 tables. Etcetera. This is not random, even if you seat all the players at table 1 "randomly" and all of the players at table 2 "randomly". The first 10 players (if you have 10-seat tables) to buy-in will all be at table 1. The second 10 players to buy-in will all be at table 2. Again, not random. Furthermore, if you end up with, say 15 players, you'll have 10 at table 1 and 5 at table 2. This will still require a balance.
2) Seat players randomly throughout all of your tables (as they buy-in). This requires only that you have an upper-limit on the number of players that will be in attendance (or that you simply have only so many tables). If you have 5 tables of 10 seats, then you know you're not going to have more than 50 players. If only 30 show up, you'll have to balance tables after everyone buys-in. THIS is how the TD behaves if you "Auto-seat at buy-in".
Oh, there is a 3rd: You know exactly who will show up, and therefore you CAN achieve a perfect random seating. In this case, don't bother with the auto-seat at buy-in. Either buy everyone in before-hand, seat everyone, then use the "Paid in Full" feature when people actually pay to buy-in. Or, allow players not bought-in to the tournament to be seated. Add everyone to the tournament, seat them, and then buy them in as they show up and actually pay.