Elxheader::TElXHeaderCellRow::Delete throws AV on Windows 7 x64

Hi,

I have some complicated header in TElXTree with joined rows. When  I try to clear this header I get AV on windows 7 x64 with message "Invalid class typecast." (on Windows 8 x64 everything seems to be ok). Here is some example project.
I try to find the source of this error in AQTime and get this call stack:

Event    Thread ID    Time
First chance exception 0xC0000005 ACCESS_VIOLATION occurred at 0x5003A358, read of address 0x00000068 at 0x5003A358 (in \LibSydel\rtl150.bpl)    4524    09:52:09:290
0x5003A358 System::AsClass + 0xC in rtl150.bpl    4524    09:52:09:290
0x008D79A5 Elxheader::TElXHeaderCellRow::Delete + 0x2D in lmdrtelcore150.bpl    4524    09:52:09:290
0x008D1498 Elxheader::TElXHeaderSections::DeleteSection + 0xA4 in lmdrtelcore150.bpl    4524    09:52:09:290
0x008D05CA Elxheader::TElXHeaderSections::Clear + 0x5A in lmdrtelcore150.bpl    4524    09:52:09:290
0x00402935 Unit1.cpp::TForm1::Button2Click + 0x49 in \Data\TElXTreeTest15\Unit1.cpp line 122 in TElXTreeTest15.exe    4524    09:52:09:290
0x5027E4DD Controls::TControl::Click + 0x75 in vcl150.bpl    4524    09:52:09:290
0x50282835 Controls::TWinControl::WndProc + 0x56D in vcl150.bpl    4524    09:52:09:290
0x502B56C1 Stdctrls::TButtonControl::WndProc + 0x71 in vcl150.bpl    4524    09:52:09:290
0x50282988 Controls::TWinControl::DefaultHandler + 0x130 in vcl150.bpl    4524    09:52:09:290
0x50282835 Controls::TWinControl::WndProc + 0x56D in vcl150.bpl    4524    09:52:09:290

Any help appreciated.