First of all, what MB5L works was that this transaction looks in the table T030, the accounts assigned to the inventory, and computes the total values based on the accounts. The values shown in the 1st column in the table, belongs to the values in the MBEW table. The FI values are build up based on the BSEG table. The point is that sometimes some postings are set in the MBEW table without being posted on BSEG (and vice versa). 

There have been several reasons which are well attributable to this problem - 

1) Change in the Valuation Class of the Material Master which results in the fact that the account determination or account used in the automatic posting was changed; 

2) Maintenance of GR/IR clearing account via Transaction MR11 after executing the month-end closing (Transaction MMPV); 

3) Adjustment of G/L account (JV process) for direct posting; 

4) Price adjustment via Transaction MR21; 

5) Manual posting of costs directly to inventory account via LIV. 

See also
Material Master Multiple Choice Questions Answers

Get help for your SAP MM problems
SAP MM Forums - Do you have a SAP MM Question?

SAP MM Books
SAP Material Management Certification, Interview and Configuration Reference Books

SAP Material Management Tips
SAP MM Configuration Tips and Materials Management Discussion Forum

Main Index
SAP ERP Modules, Basis, ABAP and Other IMG Stuff