SmallText Field too small for <JAHIA_MULTIVALUE_MULTIPLE>

If I use a selection list and allow multiple selections in a SmallText 
field (keyword: <JAHIA_MULTIVALUE_MULTIPLE>), the default values are 
written to a flat file and the database column says 
<defvalue_in_flat_file>. This is ok.

The problem is, when the user selects multiple lines, which together 
exceed 250 characters, then not all selections are stored in the database. 
Is it possible to externalize this also into a file? Should we contribute 
and do you have some hints, where to look?

Greetings,
Benjamin Papez