Unexpected behaviour difference between setProvider and setRpcProvider in TezosToolkit

[ac10n]

Consider the following code:

console.log(this.tezosToolkit.rpc.getRpcUrl())
this.tezosToolkit.setRpcProvider(this.rpcNodes[1])
console.log(this.tezosToolkit.rpc.getRpcUrl())
this.contracts[address] = await this.tezosToolkit.wallet.at(address)

This will output the following:

https://mainnet.smartpy.io/
https://mainnet.api.tez.ie/

but the network request from the final line is still sent to https://mainnet.smartpy.io/, ie the previous rpc before we called setRpcProvider

Interestingly, this.tezosToolkit.setProvider({ rpc: this.rpcNodes[0] }) works as expected.

Here we have an unexpected difference between the two APIs.
By looking at the source code of setProvider, we can see that this difference is indeed unexpected:

  setProvider({
    rpc,
    stream,
    signer,
    protocol,
    config,
    forger,
    wallet,
    packer,
    globalConstantsProvider,
    readProvider,
    parserProvider,
    injectorProvider,
  }: SetProviderOptions) {
    this.setRpcProvider(rpc);
    this.setStreamProvider(stream);
    this.setSignerProvider(signer);
    this.setForgerProvider(forger);
    this.setWalletProvider(wallet);
    this.setPackerProvider(packer);
    this.setGlobalConstantsProvider(globalConstantsProvider);
    this.setReadProvider(readProvider);
    this.setParserProvider(parserProvider);
    this.setInjectorProvider(injectorProvider);

    this._context.proto = protocol;
    if (config) {
      this._context.setPartialConfig(config);
    }
  }

The field rpc of the input parameter is only used in this.setRpcProvider(rpc);
The reason we have this difference is in the call to: this.setReadProvider(readProvider);:

  setReadProvider(readProvider?: SetProviderOptions['readProvider']) {
    const readP = readProvider ? readProvider : new RpcReadAdapter(this._context.rpc);
    this._options.readProvider = readP;
    this._context.readProvider = readP;
  }

When a readProvider is not provided, TezosToolkit will use the rpc.
In general, any call to the setProvider will call all the set***Providers, even if the calling code has not passed anything.

In my opinion, when someone passes only rpc to the setProvider, they expect only rpcProvider to be updated, and no other side effect.

How we can solve this problem?
One possible solution is to update the individual calls in setProvider like:

+    if (readProvider !== undefined) {
       this.setReadProvider(readProvider);
+    }

But this will be a breaking change: If an existing dApp called setProvider with only rpc and relied (without knowing) on the behavior that readProvder is also updated, their implementation will be broken.