Invalid access to memory - _mp_clear

<Try to describe precise steps that lead to the problem (where do you click, what keys do you press, what do you see, etc.)>
<If relevant, consider attaching a session log file or a screenshot)>

WinSCP 6.5.3

Error message:
Invalid access to memory.

Stack trace:
(00EE48DF) C5724_0
(00EF5B8E)
(00EF7C06)
(00EF49B0) __ExceptionHandler
(000B320F) ntdll.dll
(0007A66A) ntdll.dll.KiUserExceptionDispatcher
(00B60C38) _mp_clear
(00B61F2C) _mp_sub
(00B62BA8) _monty_free

(00EF61F9)
(00EF77D3)
(000CE65E) TTerminalManager::Idle
(0001CC46) TCustomScpExplorerForm::Idle
(00056D7B) TNonVisualDataModule::DoIdle
(00056D38) TNonVisualDataModule::SessionIdleTimerTimer
(00204B78) System::Classes::_18364
(00038A71) USER32.dll
(00026BE8) USER32.dll
(00026075) USER32.dll
(00025BDB) USER32.dll.DispatchMessageW

The problem happens rarely. I cannot reproduce it.

I don't click anywhere. WinSCP is constantly open because I regularly upload things to my server.
Lately, I've been getting this error without clicking anywhere.
When I come home from work, I see the error that appeared.

WinSCP 6.5.3

Error message:
Accès mémoire invalide.

Trace de la pile :
(00EE48DF) C5724_0
(00EF5B8E)
(00EF7C06)
(00EF49B0) __ExceptionHandler
(000B343F) ntdll.dll
(0007A66A) ntdll.dll.KiUserExceptionDispatcher
(00B60C38) _mp_clear
(00B61F2C) _mp_sub
(00B62BA8) _monty_free

(00EF61F9)
(00EF77D3)
(000CE65E) TTerminalManager::Idle
(0001CC46) TCustomScpExplorerForm::Idle
(00056D7B) TNonVisualDataModule::DoIdle
(00056D38) TNonVisualDataModule::SessionIdleTimerTimer
(00204B78) System::Classes::_18364
(00038B21) USER32.dll
(00026C98) USER32.dll
(00026125) USER32.dll
(00025C8B) USER32.dll.DispatchMessageW

The problem happens rarely. I cannot reproduce it.

<Try to describe precise steps that lead to the problem (where do you click, what keys do you press, what do you see, etc.)>
<If relevant, consider attaching a session log file or a screenshot)>

WinSCP 6.5.5

Error message:
Invalid access to memory.

Stack trace:
(00EE6213) C5724_0
(00EF74C2)
(00EF953A)
(00EF62E4) __ExceptionHandler
(000B332F) ntdll.dll
(0007A56A) ntdll.dll.KiUserExceptionDispatcher
(00B621A0) _mp_clear
(00B63494) _mp_sub
(00B64110) _monty_free

(00BA11C7) C4584_0
(00EF74C2)
(00EF953A)
(00EF62E4) __ExceptionHandler
(000B332F) ntdll.dll
(0007A56A) ntdll.dll.KiUserExceptionDispatcher
(00BA1241) _strbuf_chomp
(00B9FD09) _BinarySink_put_byte
(00B670F5) _ntru_encode
(00B67989) _ntru_encode_pubkey
(00B67F08) _ntru_encode_plaintext
(00B5EFE3) C4345_0
(00B5F5C3) C4345_0
(00B8359E) _ssh2kex_coroutine
(00B8EC97) _ssh2transport_finalise_exhash
(00B7DAF5) _ssh_ppl_free
(00B377B6) C4305_0
(00B378A9) _run_toplevel_callbacks
(00C9D3B1) TSecureShell::EventSelectLoop
(00C9D9ED) TSecureShell::Idle
(00D31195) TTerminal::Idle
(000CE6D1) TTerminalManager::Idle
(0001CC46) TCustomScpExplorerForm::Idle
(00056E37) TNonVisualDataModule::DoIdle
(00056DF4) TNonVisualDataModule::SessionIdleTimerTimer
(00204C90) System::Classes::_18364
(00038981) USER32.dll
(00026AC8) USER32.dll
(00025F55) USER32.dll
(00025ABB) USER32.dll.DispatchMessageW

(00EF7B2D)
(00EF9107)
(000CE71A) TTerminalManager::Idle
(0001CC46) TCustomScpExplorerForm::Idle
(00056E37) TNonVisualDataModule::DoIdle
(00056DF4) TNonVisualDataModule::SessionIdleTimerTimer
(00204C90) System::Classes::_18364
(00038981) USER32.dll
(00026AC8) USER32.dll
(00025F55) USER32.dll
(00025ABB) USER32.dll.DispatchMessageW

The problem happens rarely. I cannot reproduce it.

<Try to describe precise steps that lead to the problem (where do you click, what keys do you press, what do you see, etc.)>
<If relevant, consider attaching a session log file or a screenshot)>

WinSCP 6.5.5

Error message:
Invalid access to memory.

Stack trace:
(00EE6213) C5724_0
(00EF74C2)
(00EF953A)
(00EF62E4) __ExceptionHandler
(000B332F) ntdll.dll
(0007A56A) ntdll.dll.KiUserExceptionDispatcher
(00B621A0) _mp_clear
(00B63494) _mp_sub
(00B64110) _monty_free

(00EF7B2D)
(00EF9107)
(000CE71A) TTerminalManager::Idle
(0001CC46) TCustomScpExplorerForm::Idle
(00056E37) TNonVisualDataModule::DoIdle
(00056DF4) TNonVisualDataModule::SessionIdleTimerTimer
(00204C90) System::Classes::_18364
(00038981) USER32.dll
(00026AC8) USER32.dll
(00025F55) USER32.dll
(00025ABB) USER32.dll.DispatchMessageW

I know how to reproduce the problem or the problem happens frequently enough. I wish to be contacted by the WinSCP team to help resolving the problem.

@byrealmircea: Thanks for your report.
I have sent you an email with a debug version of WinSCP to the address you have used to register on this forum.