I'm getting the following report from FastMM's FullDebugMode after running certain queries. The relevant thing here is the stack trace. It appears that nodes are being allocated and never freed, even after the dataset is freed.

A memory block has been leaked. The size is: 68

This block was allocated by thread 0x2194, and the stack trace (return addresses) at the time was:
410AB2 [FastMM4][FastMM4.DebugAllocMem]
404A86 [System.pas][System][System.AllocMem][3549]
672AB7 [IB_NodeList.pas][IB_NodeList][IB_NodeList.TIB_NodeList.GetNewNode][517]
675B42 [IB_NodeList.pas][IB_NodeList][IB_NodeList.TIB_NodeList.AfterFetchCursorRow][1863]
6CB76E [IB_Components.pas][IB_Components][IB_Components.TIB_BDataset.AfterFetchCursorRow][33919]
6CB1FD [IB_Components.pas][IB_Components][IB_Components.TIB_BDataset.SysAfterFetchCursorRow][33784]
6BA9A8 [IB_Components.pas][IB_Components][IB_Components.TIB_Dataset.SysFetchSingle][27362]
6BA4D1 [IB_Components.pas][IB_Components][IB_Components.TIB_Dataset.FetchSingle][27192]
71AA33 [IBODataset.pas][IBODataset][IBODataset.TIBODataset.DoBeforeOpen][6649]
5863EC [DB.pas][DB][DB.TDataSet.SetActive][11311]
58624E [DB.pas][DB][DB.TDataSet.Open][11269]

The block is currently used for an object of class: Unknown

The allocation number is: 239193

Current memory dump of 256 bytes starting at pointer address 7EAC63D0:
[snipped]