Invalid access to memory

I closed a tab of a once active session. The session became inactive, so after closing the tab with the mouse wheel click the "invalid access to memory" exception appeared.

WinSCP 6.3.2

Error message:
Invalid access to memory.

Stack trace:
(001C6734)
(0009823F) ntdll.dll
(00077E51) ntdll.dll.KiUserExceptionDispatcher
(00C00184)
(00C00296)
(00C00352)
(00C966E9)
(00C96382)
(003C2CD5)
(00C962BC)
(00409261)
(003C3770)
(00D2378C)

Status: unknown_rel_addr

The problem happens rarely. I cannot reproduce it.