Here's DEF CON's statement (according to plebbit):

DEF CON thrives on community collaboration and has operated for over 30 years successfully working with hundreds of vendors including the dozens that have helped with our badges over the years. For this year’s Raspberry Pi badges, DEF CON hired Entropic Engineering to do the hardware development and firmware. After going overbudget by more than 60%, several bad-faith charges, and with a product still in preproduction, DEF CON issued a stop work order. Any claims that DEF CON did not pay Entropic Engineering for its hardware or firmware development are false. Unfortunately, we heard that these issues with Entropic Engineering were not unique to DEF CON. We decided at that point to finish the badge on our own. We paid to send engineers to Vietnam to work onsite to finalize and test the badges in order to ensure they would be done on time for the conference. We never removed Entropic Engineering’s logo from our badge, it is still on the PCB. However, Entropic was not involved in the design and production of the case, and we removed their logo we had added as a courtesy.

We were happy to still include one of their contractors on the badge panel session. Unfortunately, shortly before the talk was set to take place DEF CON became aware that unauthorized code had been included in the firmware we had paid Entropic Engineering to produce, claiming credit for the whole badge and promoting their coin wallet to solicit money from DEF CON attendees above and beyond what we had negotiated. When asked about the unauthorized code, the engineer said it had been done as a “joke” two months ago and forgot to remove it, and we decided as an organization not to have him on stage while we kept the slides in the talk giving him credit for his work. We communicated the change in advance of the talk, and this individual decided to show up for the panel anyway. He refused to leave, demanding that our security team remove him. Wanting to ensure that the other people involved in creating the badge were able to deliver their presentation, we complied with his wishes and escorted him off the stage, where he was free to continue attending the conference.

Any issues of non-payment are between him and Entropic Engineering, DEF CON fulfilled its financial obligations.

So, exactly what you'd expect hiring a company that can't market itself on merit.