Vary price for different occupancies

Can anyone help with this? I have sent messages to booking.com asking for advice but they do not seem to understand my question. they just tell me my settings are correct.

I have a small double room priced for 2 people. I give 25% discount if only 1 person staying. Children are allowed to stay free.

I have been doing this for over 2 years and it has always worked exactly as I plan, ie 2 adults pay 100%, 1 adult pays 75%, 1 adult+child pay 75%.

Recently something in the system has changed, and when potential guests search it shows the prices as follows: 2 adults 100% (which is right), 1 adult 75% (which is right), 1 adult+child 100% (I want this to be 75%)

I have not changed any settings and BDC just keep confirming my settings are correct, so I do not know why it no longer works the same way, or how to change it back.