Unexpected result when assigning a vector to itself

[jedisct1]

const std = @import("std");
const Vector = std.meta.Vector;

pub fn main() anyerror!void {
    var b = Vector(4, u32){ 1, 2, 3, 4 };
    b = Vector(4, u32){ b[3], b[2], b[1], b[0] };
    std.debug.print("{}\n", .{b});
}

Prints

{ 4, 3, 3, 4 }

instead of

{ 4, 3, 2, 1 }

Using a temporary variable produces the correct output. Is assigning a vector containing some of its own elements UB?

[daurnimator]

Possible dupe of #3696

[Vexu]

Also #3234 and #6216. In the future this will hopefully either result in a copy to a temporary like #4454 or a compile error.