Search results when "Can see forum" is only permission

Consider the following forum hierarchy and user permissions:

Forum A (top level) - User X assigned forum role of 'read only'.
Subforum B (subsidiary of Forum A) - User X assigned customised forum role of 'see only', wherein 'Can see forum' is set to 'Yes', 'Can read forum' is set to 'No'.
Sub Subforum C (subsidiary of Subforum B) - User X assigned forum role of 'read only'.

Using Advanced Search, if User X elects to search Forum A, with Search Subforums set to Yes, then matching topics within Sub Subforum C are returned.

However, if User X elects to search Subforum B, with Search Subforums set to Yes, then matching topics within Sub Subforum C are NOT returned.

It seems that by assigning User X to a forum role for Subforum B that has 'No' for 'Can read forum', then User X cannot search for content in Sub Subforum C by selecting Subforum B (and subforms) when searching. User X must select either Forum A or Sub Subforum C.

If User X selects Subforum B in Advanced Search, and elects to search subforums, then Sub Subforum C content should be returned, just as it does if User X selects Forum A.