Question for parents: When and why would you feel compelled to ignore when your daughter says she loves you?

I have been visiting my parents while I am home from college and things have been fairly harmonious. However, lately my mother does not seem to enjoy my company anymore and I do not know what I have done to provoke this. I try to be respectful (as I was raised to be) and help out around the house whenever I can. I also worked a job to try and offset the costs of me being home. Anyhow, I was on the phone with my mother today (a regular non-argumentative call) and at the end of the call I told her I loved her. She neglected to reply and hung up. Why didn't she tell me she loved me back? I really need a parents perspective here and thanks for any answers.