Testcase TC-SJ-3-12 - Join Split keys question

Dears.

 

I implemented split key and join key with GF2_8.

My implementation work fine for creating and joining of split key with GF2_8.

 

However, I tried to join key of TC-SJ-3-12 and failed to build original key.

I don't know what is wrong with my implementation.

 

Is the TC-SJ-3-12 test case right example?   

 

Sincery yours.