scenario:
crreated two identical trackers (backend sqlite)

1) created one issue with two messages in the first tracker
2) exported first tracker
3) import of the export in step 2) into the second tracker
4) added a second issue into second tracker 

a full text search now doesn't find words in the first
issue.
words occuring in the second issue are found during 
full text search

the command reindex issued in roundup-admin doesn't
change this scenario.

if you make a dump (after step 3 ) of the db file
via the sqlite command and compare the contents one gets
the following significant difference:

the db of the second tracker misses the following lines:

INSERT INTO __textids VALUES('msg',1,'summary',32);
INSERT INTO __textids VALUES('msg',1,'content',33);
INSERT INTO __textids VALUES('issue',1,'title',34);
INSERT INTO __textids VALUES('msg',2,'summary',35);
INSERT INTO __textids VALUES('msg',2,'content',36);

INSERT INTO __words VALUES('RGEFRDFEG',32.0);
INSERT INTO __words VALUES('RGEFRDFEG',33.0);
INSERT INTO __words VALUES('TTT',34.0);
INSERT INTO __words VALUES('SUCHEN',35.0);
INSERT INTO __words VALUES('EINS',36.0);
INSERT INTO __words VALUES('SUCHEN',36.0);
INSERT INTO __words VALUES('ZWEI',36.0);