<p dir="auto">The select popover gets horizontally shrunk once a value is selected</p>


<ul class="contains-task-list">
<li class="task-list-item"><input type="checkbox" id="" disabled="" class="task-list-item-checkbox" checked=""> I have searched the <a href="https://github.com/mui-org/material-ui/issues">issues</a> of this repository and believe that this is not a duplicate.</li>
</ul>
<h2 dir="auto">Expected Behavior</h2>

<p dir="auto">The popover should not get shrunk on the popover exit animation</p>
<h2 dir="auto">Current Behavior</h2>

<p dir="auto">The popover gets shrunk horizontally on the exit animation.</p>
<h2 dir="auto">Steps to Reproduce (for bugs)</h2>
<p dir="auto"><a href="https://material-ui.com/demos/selects/" rel="nofollow">https://material-ui.com/demos/selects/</a><br>
Open the select and select a value, you will see the popover is horizontally shrunk when it is exiting.</p>

<h2 dir="auto">Your Environment</h2>

<table role="table">
<thead>
<tr>
<th>Tech</th>
<th>Version</th>
</tr>
</thead>
<tbody>
<tr>
<td>Material-UI</td>
<td>latest beta</td>
</tr>
<tr>
<td>React</td>
<td>16</td>
</tr>
<tr>
<td>browser</td>
<td>Chrome 64</td>
</tr>
<tr>
<td>etc</td>
<td>n/a</td>
</tr>
</tbody>
</table>
<p dir="auto">I've just updated from beta.18 to beta.20 and my flow is breaking now:</p>
<div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content="Error: node_modules/material-ui/internal/Portal.js.flow:101
101:         return ReactDOM.createPortal(children, this.getLayer());
                                                    ^^^^^^^^^^^^^^^ null. This type is incompatible with the expected param type of
 23:     container: Element,
                    ^^^^^^^ Element. See lib: /tmp/flow/flowlib_290fc575/react-dom.js:23"><pre class="notranslate"><code class="notranslate">Error: node_modules/material-ui/internal/Portal.js.flow:101
101:         return ReactDOM.createPortal(children, this.getLayer());
                                                    ^^^^^^^^^^^^^^^ null. This type is incompatible with the expected param type of
 23:     container: Element,
                    ^^^^^^^ Element. See lib: /tmp/flow/flowlib_290fc575/react-dom.js:23
</code></pre></div>

<ul class="contains-task-list">
<li class="task-list-item"><input type="checkbox" id="" disabled="" class="task-list-item-checkbox" checked=""> I have searched the <a href="https://github.com/callemall/material-ui/issues">issues</a> of this repository and believe that this is not a duplicate.</li>
</ul>
<table role="table">
<thead>
<tr>
<th>Tech</th>
<th>Version</th>
</tr>
</thead>
<tbody>
<tr>
<td>Material-UI</td>
<td>beta.20</td>
</tr>
<tr>
<td>React</td>
<td>16.0</td>
</tr>
</tbody>
</table>