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Dimensions of representations obtained by branching rule are incorrect

Consider SO3GL3 as fixed points of the obvious involution. Then we should be able to compute restrictions of representations via the "symmetric" branching rule:

GL3 = WeylCharacterRing(['A', 2])
B1=WeylCharacterRing(['B',1])
V=GL3(3,2,-1); V.degree()

Sage says the output it 24. Now if we restrict to SO3, we get

b = branching_rule("A2","B1")
V.branch(B1, rule=b)

Sage says the output is

 B1(1) + B1(2) + B1(3) + B1(4)

and the result of

[B1(1).degree(), B1(2).degree(), B1(3).degree(), B1(4).degree()]

is

 [1, 2, 3, 4]

which is clearly wrong if dimV=24. As noted in another question ten years ago (I have too little karma to post links), Sage seems to not be able to do this properly.

Is this a problem with Sage, or am I doing something wrong?