bug: 'volume' first_issue and last_issue not returning any result

"First_Issue" and "Last_Issue"  are not returning any result. 
 
For example, if looking at Captain America Vol. 2005
Expected:
<last_issue>612</last_issue>
 
Actual:
<last_issue />
 

http://api.comicvine.com/volumes/?api_key=*removed*&offset=1000&field_list=name,last_issue,first_issue,count_of_issues,date_last_updated