Memory filling up

I have a 32 bit .exr that was output from PTGui. It is a very large image, 1.13GB, at 26396x13198 resolution.
However, as you can see from the attached screenshot, it is taking all 16GB of my memory to open it. It has been stuck at "Merging Images 50%" for over an hour now.
I don't understand how a 1GB file could use 16GB of memory so I think this is a bug.
Specifications:
SNS-HDR Home 1.4.19
Windows 7 x64
AMD Phenom II CPU
16GB DDR-3 memory
Intel SSD Hard Drive
Nvidia 460GTX graphics
I can load extremely large TIFF files in Photoshop CS5 and I do not see this error.
However, as you can see from the attached screenshot, it is taking all 16GB of my memory to open it. It has been stuck at "Merging Images 50%" for over an hour now.
I don't understand how a 1GB file could use 16GB of memory so I think this is a bug.
Specifications:
SNS-HDR Home 1.4.19
Windows 7 x64
AMD Phenom II CPU
16GB DDR-3 memory
Intel SSD Hard Drive
Nvidia 460GTX graphics
I can load extremely large TIFF files in Photoshop CS5 and I do not see this error.