Fluentui: TypeError in Panel: clientHeight of undefined

[Ryu36]

Bug Report

• __Package version(s)__: 2.7.1
• __Browser and OS versions__: Chrome 56.0.2924.87 / Windows Server 2012 R2

Describe the issue:

React Exception when using the Panel:

Exception in Panel.componentDidUpdate(): TypeError: Cannot read property 'clientHeight' of undefined
at Panel._updateFooterPosition (http://localhost:8080/vendor.js:34492:30)
at Panel.componentDidUpdate (http://localhost:8080/vendor.js:34408:18)
at Panel.obj.(anonymous function) [as componentDidUpdate] (http://localhost:8080/vendor.js:26834:42)
at measureLifeCyclePerf (http://localhost:8080/vendor.js:37907:12)
at http://localhost:8080/vendor.js:38561:11
at CallbackQueue.notifyAll (http://localhost:8080/vendor.js:23489:22)
at ReactReconcileTransaction.close (http://localhost:8080/vendor.js:43002:26)
at ReactReconcileTransaction.closeAll (http://localhost:8080/vendor.js:17485:25)
at ReactReconcileTransaction.perform (http://localhost:8080/vendor.js:17432:16)
at ReactUpdatesFlushTransaction.perform (http://localhost:8080/vendor.js:17419:20)

Panel is defined like:

<Panel headerText="New Something" isLightDismiss={true} isOpen={this.state.showNewForm} onDismiss={this.closePanel.bind(this)}>...
</Panel>

[NickSevens]

I experience kind of the same issue. However - for me it only occurs when defining multiple Panels on the page.
However the error occurs on different moments:

• When nesting 2 panels, the error occurs only when closing then parent panel
• When putting 2 panels side-by-side, the error occurs both when opening and closing the panel.

[Ryu36]

Good advice.
Another component of my site renders a second panel, too.
So I have multiple panels in one site. Assigning keys made no difference.

[micahgodbolt]

I was able to get it to repro in a codepen, so I'll check it out soon.

[dzearing]

Fix was merged.