Hello
may be this link might help:
Authorization Profile in Classification view of Material Master
This is my assumption: any user does have a "user profile". By some interaction with SAP GUI the user can store "parameters" in the profile. THis is done in the background; if the user does not check the content the he/she sometimes "forget" that there are values
Check the user with su01d look for the "parameter tab" and check content.
E.g. look here as well: Defining Settings for the Language - Variant Configuration (LO-VC) - SAP Library
May be check as well: http://www.lomag-man.org/informatique/sap%20cours/sap%20basss7-9.pdf
Quite nice kind of overview of the "user profile" settings (for old SAP system but still valid) (same as Getting Started: SAP User Settings [SAP for MIT Documentation on the Web])
C.B.
PS: check e.g. Authorization Profile in Classification view of... | SCN