Taproot 2/3 tr thresh does not work on bdk-wallet

[toskaen]

let external_descriptor = format!(
"tr({{}},thresh(2,{},{},{}))",
user_pubkey, lsp_pubkey, trustee_pubkey
);
let internal_descriptor = format!(
"tr({{}},thresh(2,{},{},{}))",
lsp_pubkey, trustee_pubkey, user_pubkey

It seems like I have to pin myself into 0.29.0 to use multi_a

why is that the case?