Yeah, I wasn't sure of your immediate needs. My experience is different scanners/models behave differently. Apparently WIA is not a lot of fun when it comes to multipage scans. You may have better luck with different hardware. I have used EzTwain Pro for many years. It is not cheap. For several years they have stuck with a flat rate and a single version that includes free updates for one year. I suspect most people do not require the very latest update each and every year. I am not affiliated and I am sure there are other products. All I can say is this is $1,000 and has worked very well for me over many years. Good luck with your project ...
http://www.eztwain.com/products.htm