I am 29 weeks and last ultrasound showed baby is and continues head down. Very uncomfortable. :-)
They can engage and pop back out again. My baby was head down at 32 weeks and she stayed that way til labour at 39 weeks.
I am 33 weeks. I have been taking prenatal classes and the instructor told us that at 32, 33 weeks babies still have room to move around and change positions so maybe your baby is playing around. But also if your baby's head is down already and it decides to stay like that it is not necessarily a sign that labor is soon. There are other signs that announce labor, maybe watch for those.