A wee bit late replying here (sorry about that) but the answer is still relevant!
This was indeed a bug that has since been fixed.
However, if you did encounter this, please send us a ticket (we have the logs to see if this happened) and we'll be able to give you an appropriate alternative reward (we won't leave you empty-handed).
If you have alliance mates that have had this problem, do encourage them to contact us via support as well!