Wireshark · Wireshark-dev: [Wireshark-dev] col_add_fstr doesn't _add_ string to column

["Wiese, Hendrik" <hendrik.wiese@xxxxxxxxxxx>]

Hi list,
 
I've got another problem here developing a dissector: why doesn't
col_add_fstr() really _add_ (append) a string to the selected column,
but clears the column and fills it with a new one?
 
I've got some TPKT encapsulated messages here inside a single TCP packet
and I'd like to get all of them displayed in the COL_INFO column one
after another. Fetching the messages out of the TPKT encapsulation
already works but only the last fetched message is displayed in the
column. So I think col_add_fstr erases the column before adding the
string. 
 
Is there any kind of 'Wireshark API' function reference somewhere on the
web? How do I really _append_ a text to a column? 

Thanks alot
 
regards,
Hendrik