TYPO3 Core

Setup:

1. Create a Fluid Template containing a simple f:switch:
   

   <f:switch expression="1">
       <f:case value="1">
           Case 1<br>
           <f:render partial="Test" arguments="{val: 1}" />
       </f:case>
       <f:defaultCase>
           Default 1<br>
       </f:defaultCase>
   </f:switch>
   

2. Create Partial Test:
   

   <f:switch expression="{val}">
       <f:case value="2">
           Case 2
       </f:case>
       <f:defaultCase>
           Default 2
           <f:render partial="Test" arguments="{val: 2}" />
       </f:defaultCase>
   </f:switch>
   

Expected output:
Case 1 Default 2 Case 2

Actual output:
Default 1

This happens because in the ViewHelperVariableContainer the `break` variable of the OriginalSwitchViewHelper is getting overridden.

I have tried the following permutations of ViewHelpers. Note: Render2 is another partial called Test2.
No Errors:
Switch -> Case -> Switch -> Case
Switch -> Case -> Switch -> Default
Switch -> Default -> Switch -> Case
Switch -> Default -> Switch -> Default
Switch -> Case -> Switch -> Case -> Switch -> Case
Switch -> Case -> Switch -> Case -> Switch -> Default

Switch -> Case -> Render -> Switch -> Case
Switch -> Case -> Render -> Switch -> Default
Switch -> Default -> Render -> Switch -> Case
Switch -> Default -> Render -> Switch -> Default

Switch -> Case -> Render -> Render2 -> Switch -> Case
Switch -> Case -> Render -> Render2 -> Switch -> Default
Switch -> Case -> Render -> Render -> Case
Switch -> Case -> Render -> Render -> Default

Switch -> Case -> Render -> Switch -> Case -> Render -> Switch -> Case
Switch -> Case -> Render -> Switch -> Case -> Render -> Switch -> Default
Switch -> Case -> Render -> Switch -> Case -> Render2 -> Switch -> Case
Switch -> Case -> Render -> Switch -> Case -> Render2 -> Switch -> Default
Switch -> Case -> Render -> Switch -> Default -> Render2 -> Switch -> Case
Switch -> Case -> Render -> Switch -> Default -> Render2 -> Switch -> Default

The following parmutations produce the error:
Switch -> Case -> Render -> Switch -> Default -> Render -> Switch -> Case
Switch -> Case -> Render -> Switch -> Default -> Render -> Switch -> Default

Now the funny part begins. This permutations produces the expected output:
Switch -> Case -> Render -> If -> Then -> Switch -> Default -> Render -> If -> Else -> Switch -> Case
Here is the fluid content for partial 'Test' for this permutation:

<f:if condition="{val} != 2">
    <f:then>
        <f:switch expression="{val}">
            <f:case value="2">
                Case 2
            </f:case>
            <f:defaultCase>
                Default 2
                <f:render partial="Test" arguments="{val: 2}" />
            </f:defaultCase>
        </f:switch>
    </f:then>
    <f:else>
        <f:switch expression="1">
            <f:case value="1">
                Case 3
            </f:case>
            <f:defaultCase>Default 3</f:defaultCase>
        </f:switch>
    </f:else>
</f:if>

But the following variant prduces the error:
Switch -> Case -> Render -> If -> Then -> Switch -> Default -> Render -> If -> Then -> Switch -> Case

<f:if condition="{val} != 2">
    <f:then>
        <f:switch expression="{val}">
            <f:case value="3">
                Case 2
            </f:case>
            <f:defaultCase>
                Default 2
                <f:render partial="Test" arguments="{val: 3}" />
            </f:defaultCase>
        </f:switch>
    </f:then>
    <f:else>
        <f:switch expression="1">
            <f:case value="1">
                Case 3
            </f:case>
            <f:defaultCase>Default 3</f:defaultCase>
        </f:switch>
    </f:else>
</f:if>

It seems that it has something to do with equal instances of the switch ViewHelper. So I tried the following code inside a partial (the template only renders the partial with val=1, without any other code in it):
Render -> Switch -> Case -> Render -> Switch -> Default -> Render -> Switch -> Case

<f:switch expression="{val}">
    <f:case value="1">
        Case 1
        <f:render partial="Test" arguments="{val: 3}" />
    </f:case>
    <f:case value="2">
        Case 2
    </f:case>
    <f:defaultCase>
        Default 1
        <f:render partial="Test" arguments="{val: 2}" />
    </f:defaultCase>
</f:switch>

Expected output:
Case 1 Default 1 Case 2
Actual output:
Default 1 Case 2

Again, this permutations work:
Render > Switch -> Case -> Render> Switch -> Default
Render -> Switch -> Case -> Render -> Switch -> Case -> Render -> Switch -> Default

Adding another Rendering with switch/case to the non working example produces the expected output again:
Render -> Switch -> Case -> Render -> Switch -> Default -> Render -> Switch -> Case -> Switch -> Case

<f:switch expression="{val}">
    <f:case value="1">
        Case 1
        <f:render partial="Test" arguments="{val: 3}" />
    </f:case>
    <f:case value="2">
        Case 2
        <f:render partial="Test" arguments="{val: 4}" />
    </f:case>
    <f:case value="4">
        Case 3
    </f:case>
    <f:defaultCase>
        Default 1
        <f:render partial="Test" arguments="{val: 2}" />
    </f:defaultCase>
</f:switch>

Expected and actual output:
Case 1 Default 1 Case 2 Case 3