Clicking back button leads to "FragmentManager is already executing transactions"

[carlastabile]

I've been following the docs to implement a Wizard but now if I click the back button the app crashes

FATAL EXCEPTION: main Process: com.minimfit.minimfit, PID: 6847 java.lang.IllegalStateException: FragmentManager is already executing transactions at android.support.v4.app.FragmentManagerImpl.ensureExecReady(FragmentManager.java:1956) at android.support.v4.app.FragmentManagerImpl.execSingleAction(FragmentManager.java:1980) at android.support.v4.app.BackStackRecord.commitNowAllowingStateLoss(BackStackRecord.java:626) at android.support.v4.app.FragmentStatePagerAdapter.finishUpdate(FragmentStatePagerAdapter.java:166) at android.support.v4.view.ViewPager.populate(ViewPager.java:1268) at android.support.v4.view.ViewPager.setCurrentItemInternal(ViewPager.java:668) at android.support.v4.view.ViewPager.setCurrentItemInternal(ViewPager.java:630) at android.support.v4.view.ViewPager.setCurrentItem(ViewPager.java:611) at org.codepond.wizardroid.Wizard$1.onBackStackChanged(Wizard.java:85) at android.support.v4.app.FragmentManagerImpl.reportBackStackChanged(FragmentManager.java:2473) at android.support.v4.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2176) at android.support.v4.app.FragmentManagerImpl.optimizeAndExecuteOps(FragmentManager.java:2103) at android.support.v4.app.FragmentManagerImpl.popBackStackImmediate(FragmentManager.java:823) at android.support.v4.app.FragmentManagerImpl.popBackStackImmediate(FragmentManager.java:776) at android.support.v4.app.FragmentActivity.onBackPressed(FragmentActivity.java:178) at android.app.Activity.onKeyUp(Activity.java:2488) at android.view.KeyEvent.dispatch(KeyEvent.java:2666) at android.app.Activity.dispatchKeyEvent(Activity.java:2741) at com.android.internal.policy.PhoneWindow$DecorView.dispatchKeyEvent(PhoneWindow.java:2310) at android.view.ViewRootImpl$ViewPostImeInputStage.processKeyEvent(ViewRootImpl.java:4127) at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:4089) at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3642) at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3695) at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3661) at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:3787) at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3669) at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:3844) at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3642) at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3695) at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3661) at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3669) at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3642) at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3695) at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3661) at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:3820) at android.view.ViewRootImpl$ImeInputStage.onFinishedInputEvent(ViewRootImpl.java:3981) at android.view.inputmethod.InputMethodManager$PendingEvent.run(InputMethodManager.java:2253) at android.view.inputmethod.InputMethodManager.invokeFinishedInputEventCallback(InputMethodManager.java:1874) at android.view.inputmethod.InputMethodManager.finishedInputEvent(InputMethodManager.java:1865) at android.view.inputmethod.InputMethodManager$ImeInputEventSender.onInputEventFinished(InputMethodManager.java:2230) at android.view.InputEventSender.dispatchInputEventFinished(InputEventSender.java:141) at android.os.MessageQueue.nativePollOnce(Native Method) at android.os.MessageQueue.next(MessageQueue.java:323) at android.os.Looper.loop(Looper.java:135) at android.app.ActivityThread.main(ActivityThread.java:5417) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

It also seems the page is not being updated when clicking the back button, this used to work with 2 pages but it crashes with more than 2