This has always been the case. Even with EVDO and 1x. When you have an active data stream going, it will want to hand off to the same technology and band. Only when it cannot find the same technology and band does it start exploring other options.
While you're in an active data stream, it just does not look and find something even niftier that may be out there. It maintains the status quo unless you no longer can keep your data stream going.
I get the same on other providers too. On VZW, it will stay on 700MHz, even when I get into AWS coverage that is faster and more robust, if I am actively in a data session. And AT&T, it will not move move WCDMA to LTE just because I drive into coverage if I am using an active data session. Not until there is a long enough pause for the device to scan or the network to shunt you, you'll stay on the current technology/band.
I'm not sure if it's limited to do that and there is no other choice, or if networks have just been set up that way. I guess that would be a good question.
I have been handed off B41 to B25 in an active data session before though. I started on B41 and drove out of B41 range and into B25. It did hand over every time. But it did not even try to connect to the really strong B25 site until B41 was unusable. It wanted to stay on B41 as long as it could.
Robert via Samsung Note 8.0 using Tapatalk Pro