Please provide the following information to reproduce the issue at our end:
1. Your OS version
2. Installed Acrobat/Reader version
3. Printer drivers and model
4. Sample PDF document on which you have observed this issue.
I am so distressed--I invested in an expensive new Canon laser printer in order to make completion of a difficult project less burdensome--and instead I am spending time I do not have trying to figure out why my Adobe pdf's will only print two-sided, which is unacceptable. There seems to be no way to undo this. I have to print one page at a time, which is a very laborious process. This must be fixable!