Possibly corrupted menu settings after saving node, using hierarchical select widget for menu - intermittent

On a client site using hierarchical select, they have had an issue a few times with nodes being inaccessible. They are unable to edit or view a node, no errors are logged, but the node data can be pulled through views.

I tracked this down to what seems to be an issue with the menu. They are saving their articles menu settings using the hierarchical select widget while editing the node. After this point, the article can be seen in its correct location in the primary links or under another item in the primary links. Normally this works, but sometimes the node becomes inaccessible.

At this point, if you edit the menu item from the main menu administration, the hierarchical select widget shows only "navigation" instead of the expected menu settinings of primary link -> sub item -> etc. Resaving the menu item from here, back to the expected menu settings, brings back the node.

Not sure if this is hierarchical selects fault or some other issue, as the bug appears to be intermittent.