You are right, this is (was) a bug showing up for sites for host-node maps, the broken implementation returns always an empty string.
So far, there are no tests in the regression tests suite that test configurations with host-node maps, so automated testing does not reveal this problem. Aside of the fact that there are some problems with the current design (see e.g. [1]), the situation gets more complicated, since NaviServer provides superior native support via multiple servers (one nsd process hosting different http servers) and virtual hosting (same server with different configurations (e.g. root directories) depending on the "host" request header field), while AOLserver does not support this (openacs.org uses this for hosting dotlrn.org). So, more work is required in this regard.
Anyhow, you showed a clear bug, this is fixed now in the oacs-5-8 branch. Many thanks for reporting.
-g
[1] https://openacs.org/forums/message-view?message_id=1529065
