PGSQL 7.4.8 : idle in transaction problem

Hello,

We are using JBOSS and postgresql on 1 database (DB1). From time to time
the JBOSS process  <idle in transaction>.

What is strange is that users on all DB (not only DB1) are affected by
the JBOSS <idle in transaction>.
I understand that it locked DB1 but why it also locked users on others DB ?

Thanks !