Having messed around with the Editor for several hours to build the Patch The World mod I posted here, perhaps I can shed some light.
There is a bug/feature in the editor such that you can only change/alter stuff in one Rules Group at a time. If you try to change things in two rule groups (say Civ Advancements and Governments) then parts of the data get "forgotten" and will henceforth be no longer accessible. This means needing to complete all interactions with a single Rules Group, Save, Quit and Relaunch every time you want to move on to a new Rules Group for editing. Failing to do this results in "null field" entries for the first item in various (if not all) Rules Groups, which if saved will become a Permanent Feature of the .bic file and cannot be corrected in edits.
One thing which I do find curious is that under no circumstances will the Palace Improvement data show up in the edit windows (no building references, no stats, nada). I suspect this has something to do with the "unique" status the Palace has with respect to the construction rules.
Another curious behavior I encountered involved the user interface "forgetting" to update the display. This has happened in two rather unusual places, the Civ Advances Screen and the Units screen. In the Civ Advances screen it was possible for individual checkboxes to stop updating their status when moving around through the Advances List. This meant that if I checked off Bridges followed by checking on Double Worker Rate (without first having checked off Double Worker for Replaceable Parts) that whenever I moved to a different Advance the Double Worker checkbox would stay checked on (whether it should be or not). I don't think the program itself believed that the checkbox had been globally checked for all Advances, but had instead "lost track" of that flag and was now simply not paying attention to to it and not updating the status to screen correctly. This behavior was also possible with the unit icons in the Units Rules, where the icons wouldn't track and update correctly when the up/down buttons were clicked. The number would change, but the icon shown wouldn't (with the first click) which in turn de-synced which icons were attached to which icon numbers.
The two behaviors were repeatable and could only by terminated (once begun) by quitting and relaunching the program. The Civ Advance checkbox problem seemed to have something to do with having boxes checked in multiple Advances when multiple Advances weren't supposed to give the same benfit (Double Workers by both Engineering and Replaceable Parts). However if the Double Workers was unchecked in Replaceable Parts then it could be checked elsewhere without causing a "hiccup" in the software.
And lastly, there appears to be a memory buffer limit to how many items can be altered in a single Rules Group at once. My mod has some rather extensive changes (nearly all units are affected in some way) and I'd nearly finished making all the changes when the response interactivity of the program started slowing. It was taking longer and longer to process changes, drop menus, etc. and just as I was almost finished the program essentially locked up entirely. I had to Force Quit to get out of it, and even then the Rules Editing Screen remained topmost (and opaque) such that I couldn't see the Force Quit screen behind it.
Right now I'd just be very happy to have Add Delete buttons added to the Units editing screen so I don't have to resort to iEditCiv for the job. This is not to say that iEditCiv is a bad piece of software, just that I'd like it to be part'n'parcel of the editor.
That and an automated Civilopedia/Pediaicons editor would be great (but that would be WORK so I'm not holding my breath for that one).
