Encountered a weird bug the other day while levelling up my Warlock in the editor. 

I took the book of wossnames ancient secrets invocation and got three free selectable cantrips. Well if I used the drop down to pick a spell D&DB would then spawn another drop down. Meaning I now had four cantrip selections.  If I picked another spell bampf! Now I could pick 5 cantrips and so on.

The  only way I found to get the phantom drop down to despawn was to set it to "choose one" then the correct number of spells would be added to my sheet but I could have added infinite spells had I so chose.

The Book of Ancient Secrets doesn’t let you pick cantrips, it lets you pick Ritual Spells. As part of the rules it allows you to add two rituals immediately and then you can add additional rituals that you find in the form of scrolls whenever you find them. Since the system has no idea when you find them, it allows you to add additional rituals immediately. That’s what the additional “phantom” dropdown is for.

Sorry I meant "Pact of The Tome"  - that gives me three free cantrips from any list. I was getting the phantom drop down on the cantrips as well. 

in The Curse of Strahd game we are playing in - the Wizard player found the same when levelling up - he could infinite cantrips too.  

In that case, please post links to both characters so the Devs can look into it.

Do they have Book of Ancient Secrets as an Eldritch Invocation? This basically lets you do the same thing as the Ritual Caster feat, and so would have the 'phantom' dropdown.