Difference between "amount in LC" in document reciept and "amount in LC" in document cancellation

Hello, experts!

I have such problem.

I have a receipt document (101 MvT) and "amount in LC" is equal 500,50 YE.

After that user cancelled this document and in cancellation document (102) we have "amount in LC" 500,40 YE.

Why we have difference in "amount in LC" between this documents?

Please can you tell me how I can solve this problem?