[GENERAL] values from txid_current()

[Sahagian, David]

Using 9.1.3

Start Transaction; DO $$ BEGIN raise info '%', txid_current(); END $$; ALTER 
TABLE MyCoolTable_1 DISABLE TRIGGER trg_foo_1 ; Commit;
Start Transaction;                                                     ALTER 
TABLE MyCoolTable_2 DISABLE TRIGGER trg_foo_2 ; Commit;
Start Transaction; DO $$ BEGIN raise info '%', txid_current(); END $$; ALTER 
TABLE MyCoolTable_3 DISABLE TRIGGER trg_foo_3 ; Commit;
Start Transaction;                                                     ALTER 
TABLE MyCoolTable_4 DISABLE TRIGGER trg_foo_4 ; Commit;
Start Transaction; DO $$ BEGIN raise info '%', txid_current(); END $$; ALTER 
TABLE MyCoolTable_5 DISABLE TRIGGER trg_foo_5 ; Commit;

Why are the Messages displayed by my pgAdmin sql window like this . . .
INFO:  7902
INFO:  7903
INFO:  7904
instead of what I expected . . .
INFO:  7902
INFO:  7904
INFO:  7906
???

Thanks,
-dvs-