Electrum 4.8.2 fixes Lightning backup bug; replace old exports

Electrum issued version 4.8.2 on Sept. 11 to repair a Lightning wallet export defect that can leave older backups unable to claim funds from anchor channels. The update restores key material that some exports deleted and adds warnings and UI limits to prevent future data loss.

The defect occurred when exported wallet files removed a randomly generated Lightning private key. That key is needed to sweep an on‑chain output after a remote close of an anchor channel; without it, an affected backup cannot spend the channel output on the Bitcoin blockchain.

Electrum’s notes and the code change identify two required conditions for the problem: the wallet used non‑deterministic Lightning keys, and the backup concerned an anchor channel. Non‑deterministic Lightning keys cannot be recreated from the wallet seed. Wallets created from BIP39 seeds or from imported extended private keys (xprvs) always produce non‑deterministic Lightning keys.

Electrum‑seed wallets are deterministic only when the wallet file was created in version 4.1 or later. Wallet files created in 4.0.x remain non‑deterministic even after the software is upgraded, so upgrading alone does not change the determinism of an existing wallet file.

Pull request PR 10851 modifies how Electrum exports Lightning-related key material by retaining the randomly generated Lightning private key in wallet-file exports. The change prevents future exports from discarding the payment key needed to claim anchor-channel funds.

The release also adds user interface protections. The individual-backup flow hides the option to request a remote force‑close when the backup cannot sweep the resulting output. On desktop, the wallet now flags Lightning channels that cannot be recovered from the seed. On Android, the channel-opening dialog warns when a channel will not be recoverable from the seed.

Maintainer SomberNight explained in the project notes that re‑enabling Lightning in an affected backup “would generate different keys, leaving its older channel-backup records insufficient to spend anchor-channel funds.” The project notes underline that an upgrade will not restore key material removed from an already exported file.

Electrum’s documented remedy asks users to update to 4.8.2 and create fresh exports from the original wallet data. The app will display a startup warning for affected wallets to prompt replacement exports. If the original wallet file needed to produce a new export is no longer available, upgrading will not recover key material that was deleted by earlier exports.

The issue applies to individual channel export files and full-wallet backups that include Lightning recovery data. Electrum’s fixes address future exports, but users holding older exported files that meet both conditions must overwrite them with newly exported backups that retain the necessary payment-key information.