Hi Julius,
really hard to find it was indeed...
the indicator was (beside the debugger) that the sql trace showed, that the abap code passed the correct data, then at the commit work 'abap' was left (still with correct data). And as Boldi stated, from the DB-interface no update was visible with that inocrrect value....
good luck, that that wise guy used lower case values for the field (which only supports uppercase form abap side), which was a good hint ...
Bernhard