In LeftInputAdapterNode a modifyByPass happens, for a sink that has not been reached before. So it thinks it's new, and thus propagates as an insert

The real bug comes in doInsertObject method. It creates a child LT here, even though once it enters doInsertSegmentMemory the mask intersect fails. This leaves a child LT, that is not propagated. Next time update is called, as the LT is there it thinks it's a modify and propagates as a modify - but it never reached the beta node or the LeftMemory, and thus the memory corruption.