Memory error preparing a report

I'm a new user to Fastreport 4 but still encountering a strange problem:

I've created a designtime TfrxReport with a design containing expressions explicit references like [frxDBDataset."CompanyID"] in the memofields
The actual dataset, resulting from a sql query and stored in a kbMemTable, is added to the report at runtime by assigning the kbmTable to the frxDBDataset.dataset property.

When i try to run report.prepare, an error is reported by FastMM ( see details below).
It looks like TfsXMLItem is freeing memory that is allocated by TDatasaet.GetFieldData [img]style_emoticons/<#EMO_DIR#>/dry.gif" style="vertical-align:middle" emoid="<_<" border="0" alt="dry.gif" /> What is going wrong here, and how can i correct it or work around it? The generation of the data and report is done in one subthread[/img]

  //
  // Generating data and storing in kbmData
  // ...

  frxDBDataset.Dataset := kbmData;
  frxDBDataset.Open;
  with aReport.EngineOptions do
  begin
    NewSilentMode := simReThrow;
    UseGlobalDataSetList := False;
  end;

  with aReport do
  begin
    EnabledDataSets.Add(frxDBDataset);
    PrepareReport(false)
  end;

FASTMM: memory manager eventlog:

--------------------------------2016/2/23 13:55:54--------------------------------
FastMM has detected an error during a FreeMem operation. The block footer has been corrupted. 

The block size is: 30

This block was allocated by thread 0xAB0, and the stack trace (return addresses) at the time was:
406C15 
40E58D 
40E6BE 
6C8890 [Data.DB.pas][Data][Data.DB.TDataSet.GetFieldData][12552]
6B6417 [Data.DB.pas][Data][Data.DB.TField.GetData][4779]
40E6BE 
6B8B26 [Data.DB.pas][Data][Data.DB.TWideStringField.GetValue][5867]
6B89EB [Data.DB.pas][Data][Data.DB.TWideStringField.GetAsVariant][5845]
1063495 [frxDBSet.pas][frxDBSet][frxDBSet.TfrxDBDataset.GetValue][354]
105E5AD [frxClass.pas][frxClass][frxClass.TfrxReport.DoGetValue][9304]
105CD5F [frxClass.pas][frxClass][frxClass.TfrxReport.Calc][8749]

The block was previously used for an object of class: TfsXMLItem

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

The allocation number is: 2038485

The block was previously freed by thread 0xAB0, and the stack trace (return addresses) at the time was:
406BC2 
409F01 
40A645 
FBB523 [fs_xml.pas][fs_xml][fs_xml.TfsXMLItem.Destroy][240]
409FFF 
FBB54C [fs_xml.pas][fs_xml][fs_xml.TfsXMLItem.Clear][247]
FBB4ED [fs_xml.pas][fs_xml][fs_xml.TfsXMLItem.Destroy][236]
409FFF 
FBB54C [fs_xml.pas][fs_xml][fs_xml.TfsXMLItem.Clear][247]
FBB4ED [fs_xml.pas][fs_xml][fs_xml.TfsXMLItem.Destroy][236]
409FFF 

The current thread ID is 0xAB0, and the stack trace (return addresses) leading to this error is:
406BC2 
40E812 
40DB02 
6C893C [Data.DB.pas][Data][Data.DB.TDataSet.GetFieldData][12559]
6B6417 [Data.DB.pas][Data][Data.DB.TField.GetData][4779]
40E6BE 
6B8B26 [Data.DB.pas][Data][Data.DB.TWideStringField.GetValue][5867]
6B89EB [Data.DB.pas][Data][Data.DB.TWideStringField.GetAsVariant][5845]
1063495 [frxDBSet.pas][frxDBSet][frxDBSet.TfrxDBDataset.GetValue][354]
105E5AD [frxClass.pas][frxClass][frxClass.TfrxReport.DoGetValue][9304]
105CD5F [frxClass.pas][frxClass][frxClass.TfrxReport.Calc][8749]

Current memory dump of 256 bytes starting at pointer address 779B63A0:
00 00 00 00 16 00 00 00 43 00 48 00 4E 00 4C 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 73 1C
D5 7A 80 80 80 80 80 80 00 00 00 00 81 64 9B 77 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
4E 93 1E 00 A6 6B 40 00 DF BC 40 00 10 BF 40 00 22 C3 FB 00 CB C3 FB 00 D9 9F 40 00 A2 C4 FB 00
A2 C4 FB 00 A2 C4 FB 00 A2 C4 FB 00 5C C5 FB 00 B0 0A 00 00 B0 0A 00 00 C2 6B 40 00 99 BD 40 00
99 DA 40 00 E1 D9 40 00 6F A0 40 00 FA 9E 40 00 45 A6 40 00 23 B5 FB 00 FF 9F 40 00 4C B5 FB 00
ED B4 FB 00 22 00 00 00 B0 04 02 00 6D 7A 99 84 8C 72 58 02 80 80 80 80 80 80 80 80 80 80 80 80
80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 92 85 66 7B 80 80 80 80 00 00 61 60 9B 77
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 4F 93 1E 00 A6 6B 40 00 DF BC 40 00 10 BF 40 00
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