DH - my brother in law's ex wife has tried to get their son away from him multiple times and it pretty much seems to be a cry for attention and power play. She wants to have all of the power when it comes to the kid, so she does whatever she can to piss the dad off. She doesn't care whether or not it is what is best for her son or not but it makes he feel better to thinks he is in control so she does whatever she can to undermine my BIL. A slight history into their relationship.... They were married for just over a year when she had their kid. A month later she comes home and tells him that she has fallen in love with someone else but she doesn't believe in divorce so if he wants his freedom he has to file. He did. She married the other guy and has in the last 2 years that I've known her had 4 affairs, 2 of which have included moving out for at least a month. Taking her now 5 year old with her.
Some people are just assholes and/or unbalanced.