Invalid access to memory - @Tb2toolbar@TTBToolbarView@DoUpdatePositions$qqrr19System@Types@TPoint

<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 6.1.2

Error message:
Invalid access to memory.

Stack trace:
(003985B7)
(000878AF) ntdll.dll
(00073EE1) ntdll.dll.KiUserExceptionDispatcher
(003998E7)
(004E2852) @Tb2toolbar@TTBToolbarView@DoUpdatePositions$qqrr19System@Types@TPoint
(004D43F0) @Tb2item@TTBView@UpdatePositions$qqrv
(004CE1DC) @Tb2item@TTBCustomItem@InternalNotify$qqrp21Tb2item@TTBCustomItemi28Tb2item@TTBItemChangedActionit1
(004CE22D) @Tb2item@TTBCustomItem@Notify$qqr28Tb2item@TTBItemChangedActionip21Tb2item@TTBCustomItem

(002939E8)
(000878AF) ntdll.dll
(00073EE1) ntdll.dll.KiUserExceptionDispatcher
(004E2852) @Tb2toolbar@TTBToolbarView@DoUpdatePositions$qqrr19System@Types@TPoint
(004D43F0) @Tb2item@TTBView@UpdatePositions$qqrv
(004CE1DC) @Tb2item@TTBCustomItem@InternalNotify$qqrp21Tb2item@TTBCustomItemi28Tb2item@TTBItemChangedActionit1
(004CE22D) @Tb2item@TTBCustomItem@Notify$qqr28Tb2item@TTBItemChangedActionip21Tb2item@TTBCustomItem

(002939E6)
(000878AF) ntdll.dll
(00073EE1) ntdll.dll.KiUserExceptionDispatcher
(000878AF) ntdll.dll
(00294ACA)
(000878AF) ntdll.dll
(00073EE1) ntdll.dll.KiUserExceptionDispatcher
(003998E7)
(004E2852) @Tb2toolbar@TTBToolbarView@DoUpdatePositions$qqrr19System@Types@TPoint
(004D43F0) @Tb2item@TTBView@UpdatePositions$qqrv
(004CE1DC) @Tb2item@TTBCustomItem@InternalNotify$qqrp21Tb2item@TTBCustomItemi28Tb2item@TTBItemChangedActionit1
(004CE22D) @Tb2item@TTBCustomItem@Notify$qqr28Tb2item@TTBItemChangedActionip21Tb2item@TTBCustomItem

The problem happens rarely. I cannot reproduce it.