When you view ANY of the CODEX in the Dormizone, the back button doesn't take you back to the list of panels, but exits the CODEX.
The Back Button or ESC should take you back one menu level to the list of panels.
It does behave properly in the Ship CODEX reached via the Quest Station.
Steps to reproduce
Enter the Dorminzone
Go to the CODEX "Lost Islands of Duviri"
View any Codex entry and press the back button or hit ESC
This will exit the CODEX and you have to re select the CODEX to view another entry.