No subject

That could be one reason. Could I ask you to conduct the same test and
supply the log, but using another frontend, perhaps Xsane? Also with
debugging (SANE_DEBUG_HP5590=50) enabled.

Anyway, the log looks normal for me, except for scanner failed to
start scanning operarion for 2nd page.

Next step would be to gather Usbsnoop log from Windows machine during
the same operation. Do you have Windows installed on some machine
where you could do that?

-- 
 Ilia Sotnikov