!2096 (merged) split the Spin button into separate Spin and Shield buttons, placing Shield on LB by default. This merge request moves Shield to B, so that the "main buttons" are all face buttons (A for Jump, X for Spin, B for Shield).
In the process, it moves Custom 1 from B to Y, Custom 2 from Y to LB, Toggle First-Person from D-Pad Down to RS, Next Viewpoint from RS to D-Pad Up, and Toss Flag from D-Pad Up to D-Pad Down (because that you "place the flag down").
This means that camera control is now all on the right hand (Right Stick, RS, and RB), and the D-Pad is now all Ringslinger-/Multiplayer-related. Custom 2 doesn't have a similar "good reason" to be on LB, besides just "you can use it while on the move, and there are no other free buttons for it".
In particular, this means that if someone has the default controls from v2.2.13 and set "Controls per Key" to "Several", the Shield button will now conflict with Custom 1 (which is okay in vanilla SRB2) instead of Toggle First-Person. The first point of #1152 (closed) still applies, though, and Shield still won't have a gamepad default with an old config where "Controls per Key" is set to "One".
These images show the old and new gamepad defaults, with the changes since v2.2.13 highlighted:
