TYPO3 Core

Thanks for your reporting, I have found the problem or differences.
The method AbstractCondtionViewHelper::renderThenChild is different and renders in 4.5 the other children nodes if no "then"-node is available.

Test cases:

    <f:if condition="1">
        <p>should be visible, because no f:then or f:else here </p>
    </f:if>
    <f:if condition="1">
        <f:then>
        <p>should be visible, because only one f:then here </p>
        </f:then>
    </f:if>
    <f:if condition="1">
        <f:else>
        <p>should NOT be visible, because no f:then and only one f:else here </p>
        </f:else>
    </f:if>
    <f:if condition="1">
        <f:then>
        <p>should be visible, because f:then and f:else here </p>
        </f:then>
        <f:else>
        <p>should NOT be visible, because f:then and f:else here </p>
        </f:else>
    </f:if>
    <f:if condition="0">
        <p>should NOT be visible, because no f:then or f:else here </p>
    </f:if>
    <f:if condition="0">
        <f:then>
        <p>should NOT be visible, because only one f:then here </p>
        </f:then>
    </f:if>
    <f:if condition="0">
        <f:else>
        <p>should be visible, because no f:then and only one f:else here </p>
        </f:else>
    </f:if>
    <f:if condition="0">
        <f:then>
        <p>should NOT be visible, because f:then and f:else here </p>
        </f:then>
        <f:else>
        <p>should be visible, because f:then and f:else here </p>
        </f:else>
    </f:if>