
And here's what the image looks like if I remove alpha channel.

(Unfortunately the buggy(?) file is about 7MB in size and I don't have a host that would accept it (photobucket converts it to jpg automatically.)
Zooming close enough (150% or more) also fixes the issue. Converting the file to PNG with ShellEx creates a mostly white image that's completely broken (zooming doesn't help anymore and there's no alpha channel to remove). Converting to other formats (that I tested) behaves in similar fashion to the original BMP while conversion to JPG "fixes" it.
If the grayness is correct, then zooming close enough and the gray disappearing is the buggy part. Also, the PNG losing the alpha channel (if there ever was one) is another issue.