I've found that I ordered a book twice without knowing that (the button was not greyed out). Just wrote an email to Logos sales department, asking for a refund.
If you are purchasing Christmas discounted books one by one, or in small sets like me, remember to double check your orders - or keep track somewhere in an alphabetically sorted file.
To the developers of logos.com website: The website software doesn't warn me about books I own, even in checkout step. I think that could be improved. During checkout you don't have to spend many resources to query the licenses that I own...
I cannot understand this kind of bug, since I am a programmer myself.
At least a warning could help.
