user9382: Electrum 2.0 has been causing me some frustration, insofar as it seems to be a non-standard implementation of BIP32/BIP39 (HD wallets, mnemonic seed, respectively). The wallet in question is a 2of2 multisig wallet (all P2SH), with the 2nd extended public key being created in pybitcointools using 
bip32_privtopub( bip32_master_key( sha256("a password") ) ), 
then imported into Electrum.
Given the 13 word seed, which itself is non standard since the last word is a checksum, it's proven impossible to export the xpriv key from Electrum. 
How is a mnemonic seed converted to a BIP32 standard extended private key (given the client itself won't allow it)? : EDIT1: with great difficulty, see my answer below
(REFOCUSED) QUESTION: *why does Electrum:

stray from BIP0039?
make exporting the master BIP32 private key impossible?
return partially signed P2SH hex Txs which are malformed?


user25088: There is an alternative way to extract the master extended private key (xprv): in the Electrum console, simply type this:
wallet.get_master_private_key('x/', gui.password_dialog())

Or for the master private key of a wallet created with Electrum 1.x, it's:
wallet.get_seed(gui.password_dialog())

Warning
Don't ever type your password or a private key into the console. In other words, don't do this:
wallet.get_seed('my-password')

Everything you type into the console is temporarily stored inside your wallet file unencrypted to make the command history feature (accessed via the up-arrow) work.

user54292: Note: July 2017, Electrum v2.8.3... the command is now:
getmasterprivate()

The password dialog box will automagically pop up ;)

user7267: Thomas Voegtlin , the developer of Electrum explains the reasoning in the first 10 minutes of this interview. I think he also posted same thing to Bitcoin dev mailing list some time ago.
https://letstalkbitcoin.com/blog/post/epicenter-bitcoin-69-thomas-voegtlin-electrum-spv-wallets-and-bitcoin-aliases
His main point against BIP39 is that it doesn't include a version number, and the requirement of the word list dictionary in order to implement it. 

9382: <p>Electrum 2.0 has been causing me some frustration, insofar as it seems to be a non-standard implementation of BIP32/BIP39 (HD wallets, mnemonic seed, respectively). The wallet in question is a 2of2 multisig wallet (all P2SH), with the 2nd extended public key being created in <em>pybitcointools</em> using </p>

<p><code>bip32_privtopub( bip32_master_key( sha256("a password") ) )</code>, </p>

<p>then imported into Electrum.</p>

<p>Given the 13 word seed, which itself is non standard since the last word is a checksum, it's proven impossible to export the <code>xpriv</code> key from Electrum. </p>

<p>How is a mnemonic seed converted to a BIP32 standard extended private key (given the client itself won't allow it)? : <strong>EDIT1</strong>: <em>with great difficulty, see my <a href="https://bitcoin.stackexchange.com/a/36840/9382">answer</a> below</em></p>

<p><strong>(REFOCUSED) QUESTION</strong>: *why does Electrum:</p>

<ul>
<li>stray from BIP0039?</li>
<li>make exporting the master BIP32 private key <em>impossible?</em></li>
<li>return partially signed P2SH hex Txs which are malformed?</li>
</ul>
 25088: <p>There is an alternative way to extract the master extended private key (xprv): in the Electrum console, simply type this:</p>

<pre><code>wallet.get_master_private_key('x/', gui.password_dialog())
</code></pre>

<p>Or for the master private key of a wallet created with Electrum 1.x, it's:</p>

<pre><code>wallet.get_seed(gui.password_dialog())
</code></pre>

<h3>Warning</h3>

<p>Don't ever type your password or a private key into the console. In other words, don't do this:</p>

<pre><code>wallet.get_seed('my-password')
</code></pre>

<p>Everything you type into the console is temporarily stored inside your wallet file <em>unencrypted</em> to make the command history feature (accessed via the up-arrow) work.</p>
 54292: <p>Note: July 2017, Electrum v2.8.3... the command is now:</p>

<pre><code>getmasterprivate()
</code></pre>

<p>The password dialog box will automagically pop up ;)</p>
 7267: <p>Thomas Voegtlin , the developer of Electrum explains the reasoning in the first 10 minutes of this interview. I think he also posted same thing to Bitcoin dev mailing list some time ago.</p>

<p><a href="https://letstalkbitcoin.com/blog/post/epicenter-bitcoin-69-thomas-voegtlin-electrum-spv-wallets-and-bitcoin-aliases" rel="nofollow">https://letstalkbitcoin.com/blog/post/epicenter-bitcoin-69-thomas-voegtlin-electrum-spv-wallets-and-bitcoin-aliases</a></p>

<p>His main point against BIP39 is that it doesn't include a version number, and the requirement of the word list dictionary in order to implement it. </p>
