Subject Oldest transaction don't change


i have a strange thing with a superver 2.5.2 on windows.

when i do a simple query on a table and after ask for db stat the Oldest 
transaction counter don't up and i'm sure that the transaction is no longer 
active because
1) select count(1) from mon$transactions => 0.
2) and i don't have any attachement to the db after each request.

so for exemple my dbstat begin like that :

Oldest transaction	1
Oldest active		2
Oldest snapshot		2
Next transaction	3

and if i do 10 select the result is :

Oldest transaction	1
Oldest active		12
Oldest snapshot		12
Next transaction	13

my request id done via node-firebird :
to do the request it connect to the db, execute the statement, and close 
the connection and it uses the remote protocol.

the server don't seem to be more slow.
the main problem is that the sweepeer do sweeep all the time :(
have you an idea on what happen ? (in 2.5.3, i don't have this problem)