As I'm browsing area51 I see unapproved posts. When I go to approve them, I click the approve/moderate link in viewtopic. This sends me to MCP with approve/reject buttons, I select approve, the post is approved and I am presented with two links: "return to previous page" and "return to the post".

The "previous page" is "topics awaiting approval". Note that I never actually was at that page. I went from viewtopic to "approve details". Therefore this behavior is objectively incorrect.

Furthermore, subjectively I never cared for being in MCP. I browse the forum and I approve a post there, I want to return back to the forum to continue browsing. (Or in my case active topics.) The fact that I see an MCP view as one of the intermediate steps does not change the fact that logically for me "back to the previous page" is "back to where I was before, i.e. viewtopic".