6 month old puppy peeing on her bed

Question
Hello,

My boyfreind and I recently adopted a 6 month old amstaff/lab mix.   She is an amazing puppy, very obediant and a quick learner.  She is a rescue dog from a shelter where they crate trained her for bed time.  We are crate training her for bed and for home alone times. She has taken really well to this and had few accidents in the times we have left her alone.  What keeps happening is she will walk right into her crate (while I'm in the next room) and pee on her bed, grab a toy and walk away like nothing happend.  When she is not in her crate she lets me know when she has to go.  She walks over to the door and scratches on it.  She does this weird behavior with no warning.  She enjoys being in her crate and has no problems sleeping on her bed.  I am getting frustrated with buying her new beds and am wondering if you have any advice for me.  

Thanks!
_Illana  

Answer
I would recommend having a urine sample checked to rule out any underlying urinary tract infection.

Secondly, I would NOT put a bed in the crate.

Take her outside every few hours and praise her and reward her when she urinates...use a special treat such as a piece of hot dog or chicken breast.