unsigned transaction size differs on import to offline machine

Generating a transaction on my online watch wallet I get a size of 2000-something, but when I transfer to my offline signing wallet I get a size of 3000-something pre-signing (a good couple hundred greater!)!. Same versions of electrum. I saved the tx from online machine by copying to clipboard and saving to a text file.

For investigative purposes I created a watch wallet on the offline machine, and strangely when I import the unsigned transaction to this watch wallet, the transaction size appears correctly!

The unsigned transaction involves an old non-segwit address sending multiple outputs to a segwit address.

Obviously the differential in transaction size means the fee rate is wrong, so this seems like a bug.

Any assistance would be appreciated re ensuring I'm signing the right transaction (the size differential has monkey-wrenched this).

Possibly related issue: https://github.com/spesmilo/electrum/issues/6671

The report names no files, tests, or entry points. Start by reviewing the unsigned-transaction import path and the related issue #6671, then compare size and fee-rate handling for old non-segwit inputs sending to segwit outputs. Done means the transaction size remains consistent between online and offline wallets before signing.