Have you thought about using GDAL to mosic  them.

It is free and easy. First link.

For Windows OS us the OSGEO4W install.

http://www.gdal.org/gdal_merge.html

http://trac.osgeo.org/osgeo4w/

Thanks Stuart.  I will try GDAL.  But is there a way to use ERDAS mosaic without this issue persisting?

Thanks Cristina.  No, I didn't apply the "seamline" functions of the ERDAS MosaicPro.   So my problem is not really about the edges.  Overlapping edges of the images are fine with me.  The problem is on the pixel values.  As I mentioned above, the input images were in 'float' type (0 to 1), but after I mosaic the images, the pixel values became integers -- not just with the overlapped edges but with all the pixels in the all images.  Everything just changed!   So, my question is, how will i retain the float type in my final mosaic image?

Hi Cristina.  I will try and run the process again.  I have 19 images to mosaic together. 

No color corrections -- no histogram matching, no image dodging, no feathering

In the 'set overlap function' i use the default 'overlay'

In the 'output image options'  i use the defaults "Union of all inputs" with output data type 'float single'. No rescaling.

In the 'output options', i use the defaults too: Ignore input values = 0, output background values = 0.

Mosaic is running now and i will update you of the output.