I requested a book on Monday. on Tue there is a 'accepted-printed' message for the book. then on Wed same thing again. accepted-printed. Now this morning Thur same thing again. accepted-printed. How long can they keep doing this?

Sounds like a glitch to me...I would contact PBS.

I may be wrong, but I think it just means that the person printed a regular label without using printed postage. If you hover your mouse over the exclamation point, it should tell you the date the package has to be marked mailed.

Yes, I have one like that now.  I thought it just stays at that status until it is marked mailed.

It means that the person accepted the request and then immediately printed the mailing label.  I do this all the time.  I pull the book, then accept the request and print the label.  One still has five days to mail the book, if need be.