I have not seen this issue before where the size is larger then what was created. Seeing that you tested with both File and Block IO I can't imagine how it would increase the values.
Does this happen if you test with just a Microsoft system using the MS iSCSI initiator?
Not sure why as well. Unless there is a Virtual Iron initiator setting that you can match with ours. You can go to the console and enter CTRL + ALT + W then Tuning options then iSCSI daemon options then select the Target and compare with Virtual Iron.