Transaction Serialization/Deserialization not matching

Question

I'm trying to send a serialized transaction to a server, and then deserialize it there to be sent to an RPC then.

There's one owner account, and two types of instructions as mentioned:

• NonWritableIx: this instruction does NOT require owner to be isWritable: true
• WritableIx: this instruction does require owner to be isWritable: true

Now if a send a serialized Transaction(NonWritableIx, WritableIx), and then deserialize it in the server, I notice that the owner account is marked as isWritable: true even for the NonWritableIx.

Whereas if I send a serialized Transaction(NonWritableIx, NonWritableIx), then on deserialization, both instructions have owner as isWritable: false.

I'm assuming in the former case, the isWritable changes due to the presence of a WritableIx. But I was wondering if this is a desired behaviour?

The code snippet for serialization/deserialization is as shown below,

// Client
 const serialized = tx.serialize({
     requireAllSignatures: false,
 });

// Server
const serialized = request.body?.transaction;
if (typeof serialized !== 'string') throw new Error('invalid transaction');
let transaction = Transaction.from(Buffer.from(serialized, 'base64'));

Answer 1

When a transaction is serialized, the writeable and signer bits are only stored once for each account, at their most promoted value as referenced by all instructions. This discards the individual instruction-specified values making it impossible to recover upon deserialization.