To reproduce the problem:
1. Start Toad and make a connection using a 19c client and make a note of memory usage.
2. Open the editor
3. Run a select statement that returns a lot of LOB values, for example: Select * from SYS.WRI$_SQLSET_PLAN_LINES
4. Scroll down in the grid until memory usage is significant, at least 1Gb.
5. Close the editor and note memory usage. Without the leak, memory usage should be close to what it was in step 1. With the leak, memory usage goes down but is significantly higher than in step 1.