Finding elements by pattern availability

Following code does not work as expected, i.e. returned element does not implement Dock pattern. Is it FindFirst API limitation or bug?

CoInitializeEx(NULL, COINIT_MULTITHREADED);

CComPtr<IUIAutomation> automation_ptr;
HRESULT hr = automation_ptr.CoCreateInstance(__uuidof(CUIAutomation), NULL, CLSCTX_INPROC_SERVER);

IUIAutomationElement *root_element_ptr;
hr = automation_ptr->GetRootElement(&root_element_ptr);

VARIANT prop;
prop.vt = VT_BOOL;
prop.boolVal = 1;

IUIAutomationCondition* condition_ptr;
hr = automation_ptr->CreatePropertyCondition(UIA_IsDockPatternAvailablePropertyId, prop, &condition_ptr);

IUIAutomationElement* element_ptr = NULL;
hr = root_element_ptr->FindFirst(TreeScope_Descendants, condition_ptr, &element_ptr);

VARIANT check;
hr = element_ptr->GetCurrentPropertyValue(UIA_IsDockPatternAvailablePropertyId, &check);