DPII, actually, the reason why I picked banking as a "AND" tech prereq for masonry is because masonry isn't a prereq tech for any of the banking prereq techs.
The reason why I am bringing this issue up is because I am finishing up the tech tree editor and I stumbled across this issue. At first I though I had messed something up in my own code after a few hours of bashing my head into a wall I decided to see if this happens in regular Civ4 and guess what? It does and it also happens in Warlords.
Here are the steps to reproduce the bug:
1) Add TECH_BANKING as a "AND" prereq to TECH_MASONRY
2) Start a regular single player game
3) Bring up the tech chooser in the game (F6)
4) Select Masonry in the tech chooser and the game will crash without any type of warnings, errors, etc. in the logs