BDE against Interbase

I have a multi-threaded database application with 6 threads working with
an Interbase database through TDataModules. No IBExpress component is
used.
On each DML (insert, update, delete) which gets issued to the database,
an amount of memory (at least 100k) gets allocated, and never be freed
until the end of session.
This causes a windows blue page error and will terminate my application
after some minutes. Because the application issues a DML every 2
seconds.
What is the problem. Note: I do not want to use IBExpress.
Thank you.