scanning preview too small

[designerdoofus]

I have a Photosmart C150 and a mac OS X, version 10.4.11.  I have a number of small objects (different sized leaves) that I am scanning with destination from dropdown as Jpeg to HP Photosmart or as Jjpeg to IPhoto. Sometimes I cannot accept the first scan, as they are overlapping and need to be readjusted on the glass plate. When the preview looks good,  then I save to the above destinations. 

At first it was working fine, i.e.,scanning and saving all the leaves on the glass plate.  Lately it has been cropping out part of the objects, either as a small or larger box, typically in the middle of the preview . Even if I pull the "marching ants" perimeter toward the outer margins of the preview rectangle (the scanning area)and then accept the scan, it will show up in the destination (either iphoto or  HP) as just part of the image. 

Reading about resizing in Help, I went into Basic, chose resize to change the "selection area dimension" to 8.5 x 11.69 and clicked the lock shut, then rescanned.  While it is scanning , I can watch the HP Scan Pro "selected Image properties" change from 8.5 x 11.69 to something else, and the picture has cropped out areas again.   When I  click on Basic and resize  again, the lock is open and the dimensions changed to something else again.

What am I doing wrong?  Is the scanner getting confused due to multiple small objects being scanned at once?  Why was it working correctly before?  Is there a way I can trick it into behaving?