Crash when trying to return BlocklyFragment from the back stack

I have AppCompatActivity with NavigationDrawer having three items. I select one simple fragment, then go to the fragment extending AbstractBlocklyFragment, then select another simple fragment and then press back. The app crashes with the following text:

...E/InputEventSender: Exception dispatching finished signal.
...E/MessageQueue-JNI: Exception in MessageQueue callback: handleReceiveCallback
...E/MessageQueue-JNI: java.lang.IllegalStateException: This flyout is already initialized!
at com.google.blockly.android.FlyoutFragment.init(FlyoutFragment.java:175)
at com.google.blockly.android.control.FlyoutController.setTrashUi(FlyoutController.java:207)
at com.google.blockly.android.control.BlocklyController.setTrashUi(BlocklyController.java:300)
at com.google.blockly.android.control.BlocklyController$Builder.build(BlocklyController.java:2063)
at com.google.blockly.android.BlocklyActivityHelper.<init>(BlocklyActivityHelper.java:157)
at com.google.blockly.android.AbstractBlocklyFragment.onCreateActivityHelper(AbstractBlocklyFragment.java:193)
at com.google.blockly.android.AbstractBlocklyFragment.onCreateView(AbstractBlocklyFragment.java:99)
at android.support.v4.app.Fragment.performCreateView(Fragment.java:2337)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1419)
at android.support.v4.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManager.java:1740)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1809)
at android.support.v4.app.BackStackRecord.executePopOps(BackStackRecord.java:857)
at android.support.v4.app.FragmentManagerImpl.executeOps(FragmentManager.java:2577)
at android.support.v4.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2367)
at android.support.v4.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManager.java:2322)
at android.support.v4.app.FragmentManagerImpl.popBackStackImmediate(FragmentManager.java:851)
at android.support.v4.app.FragmentManagerImpl.popBackStackImmediate(FragmentManager.java:794)
at android.support.v4.app.FragmentActivity.onBackPressed(FragmentActivity.java:172)
at android.app.Activity.onKeyUp(Activity.java:2506)
at android.view.KeyEvent.dispatch(KeyEvent.java:2633)
at android.app.Activity.dispatchKeyEvent(Activity.java:2757)
at android.support.v7.app.AppCompatActivity.dispatchKeyEvent(AppCompatActivity.java:534)
at android.support.v7.view.WindowCallbackWrapper.dispatchKeyEvent(WindowCallbackWrapper.java:58)
at android.support.v7.app.AppCompatDelegateImplBase$AppCompatWindowCallbackBase.dispatchKeyEvent(AppCompatDelegateImplBase.java:316)
at android.support.v7.view.WindowCallbackWrapper.dispatchKeyEvent(WindowCallbackWrapper.java:58)
at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchKeyEvent(PhoneWindow.java:2297)
at android.view.ViewRootImpl$ViewPostImeInputStage.processKeyEvent(ViewRootImpl.java:3995)
at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:3957)
at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3488)
at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3541)
[...]

That's how I put transactions into manager:

private fun setFragment(fragment: Fragment) {
        supportFragmentManager.beginTransaction()
                .replace(R.id.content_frame, fragment)
                .addToBackStack(null)
                .commit()
    }

google / blockly-android

Crash when trying to return BlocklyFragment from the back stack #658