The complexType VisualforcePage was added to the Winter '16 Partner API in v35.0. In v34.0 and earlier it didn't exist.
<element name="showLabel" type="xsd:boolean"/>
<element name="showScrollbars" type="xsd:boolean"/>
<element name="suggestedHeight" type="xsd:string"/>
<element name="suggestedWidth" type="xsd:string"/>
<element name="url" type="xsd:string"/>
This element shouldn't be coming back with API calls using v34.0 or earlier. A support case should be raised so the API team can resolve it.
Update from support for Case# 12570930
I have created this new case to address your query related to the version regression that we see in the Winter '16 Partner API call which is part of the describeLayout() call.
The calls shouldn't show up in older API versions and the R&D has logged a bug to address this issue.
R&D confirmed that this bug related to the new VF type for describeLayout() call in the v35 Partner API will also be addressed in the patch fix that we are going to have on 10/06[/15].