According to @pod2g, a new version of Corona jailbreak will be released soon to Cydia in order to fix the iBooks DRM issues. iBooks never played well on our jailbroken device. Hopefully the new version will indeed fix this issue as pod2g pointed in his twitter:
For those of you that don’t know, Corona is an untether jailbreak tool that available on Cydia, hint, you will need it only if you’re on 5.01 with a tethered jailbreak. I would recommend to restore your 5.01 device and jailbreak using the latest version of redsn0w (untether).