In Update 10, the problem with the inability to buy David out remains.
Viewing post in Male's Hunter Daily Adventure comments
It's so strange because before launching this new release, I simulated a new game... I played through the whole story of Paul and David... and everything was fine. Even though I bought Paul first, I was able to go back to the auction, and when it was David's turn, the option to bid on him appeared as normal... I did... and bought both of them.
I couldn't repeat the error you're describing, so I can't figure out where the problem might be.
If you can repeat the story and give me a detailed step-by-step description of what you did and what exactly happens, so I can replicate it here.
I bought one (Paul) the first time and had a meeting with him (using the softest possible scenario). Then I repeated the same with David - bought him and had a "soft" meeting with him. Then I completely finished Paul's story using the "love" scenario. After that, you can't buy David back any time you visit the auction. I can provide a save file if that helps.