What steps will reproduce the problem?

1. Create a (TMAPI 2.0) TopicMap object that accesses a PostgreSQL backend as 
described in 
http://code.google.com/p/ontopia/wiki/TMAPI2 ("How to access the 
implementation")
2. Change the topic map, e.g. 
    Topic t = tm.createTopic();
3. Close the topic map
    tm.close();

What is the expected output? What do you see instead?

Changes to the topic map via TMAPI are not committed to the database. It is 
possible to commit 
by converting the TopicMap object into a TopicMapImpl object, get its wrapped 
TopicMapIF and 
call the stores commit function:

TopicMapIF tmif = ((TopicMapImpl)tm).getWrapped();
tmif.getStore().commit();

As long as TMAPI has no native support for committing changes, at least 
TopicMap.close() and 
TopicMapSystem.close() should commit the transaction. Maybe TopicMapImpl could 
have a non-
TMAPI commit() function to allow committing changes without the need to either 
close the 
TopicMap object or convert into a TopicMapIF.

TMAPI calls should NOT always call commit(), as this will have performance 
issues (as pointed out 
by Lars Marius).