Why is it necessary to use a common LUT with 16-bit and IKONOS multi-segment imagery?
Basically, a 16-bit (or 11-bit treated as 16-bit) data cannot be displayed on a 256 grey-level color gun, so IMAGINE generally bins the data for you into 256 bins.
Where the bins occur depends upon the distribution of the input image. Even if you Direct Bin the data (as many bins as max - min), the binning occurs between the minimum and maximum data values for that image. Consequently two 16-bit images generally don't have the same binning structure and therefore it's difficult to copy breakpoints from one to another (because the breakpoint in one might not exist in the histogram of the other!).
The ideal solution is to mosaic the two halves back together again once you've received them. Then you would have no problems. A single LUT could be used for the image mosaic.