Yeah there's currently a bug with mirror mode and walking tile flags (obstacles etc) it happens completely randomly, so sometimes it works fine but if it ends up loading the region incorrectly.. then bug
it currently affects most walking-related scripts such as combat scripts etc, motherlode mine (with the rockfalls), stronghold (with all the doors)
MGI has been notified of this and he said there will be a fix in the next version of mirror mode
Here is the thread: http://osbot.org/forum/topic/90826-edit-mirror-issue-flags-arent-getting-updated/
With injection mode it works like a charm though, I have been running it in stealth injection and so far so good