All of the code that parses the response from Flickr is conditional.
The code that sets the description reads as follows:
if (reader.LocalName == "description")
Description = reader.ReadElementContentAsString();
This only moves the XmlReader on if the current element is a description element. Otherwise it leaves it where it is and is processed for this Photo instances ends.
There are numerous unit tests that double check this is working correctly (i.e. if you ask for 10 photos you get 10 back) as it did take me a while to get it right, but as such I can guarantee you that it does not 'skip' photo elements at all.