There seem to have been some changes in the map builder in Crusade, possibly the game (the two operate a little differently) with regard to systems. I am not documenting these well in my modding, so I thought I'd post what I know here as a resource for other modders.

 UPDATES BELOW: Many of my recent issues were due to a coding error... as usual.

MORE UPDATES!

This is my list so far:

Defaults, at least the one I can recall:

• an empty 'star lane' puts in a 'YellowStar';
• an empty 'asteroid' lane has an approximately 1/10 chance of having an asteroid field in it. Not sure if this changes with asteroid abundance settings;
• a star has a radius of about 80, it will 'leak' out into the surrounding hexes. I use 70 as a cut-off;
• a star or particle effect that extends past the hex the star is in has no effect on those hexes. That means a planet or ship can be 'hidden' by the star. You can still see it when you zoom out to strategic icons, and you can still click it, etc., it will just be difficult to see;
• an empty 'no random' lane obviously has nothing in it. AFAIK, empty 'Star,' 'DeadZone,' 'HabitableZone,' and 'OuterZone' lanes do the same;
• you do NOT have to have a 'star' lane. The first lane will just be one hex. I have no idea what happens if you just have random planets in it... that wasn't worth checking;
• the object (unary or binary) in the first lane is named as the star, everything else is named as planets regardless of their type;
• default planet suffix above X (or is it XII?) goes from Roman to Arabic numerals;
• you can mod the binary star and planet naming suffixes (sufficies?!?!), and add suffixes for higher-number planets;
• binary stars appear to distort the shapes of lanes into ovals. I'm not positive on this; - at most only the inner rings, the outer ones are +2 rings from the center hex;
• you CAN put bodies other than those expected for a lane in that lane, but max/ min planets only refers to the type for that lane;
• max/ min planets does nothing in an 'Asteroid' or "NoRandom' lane;
• you can leave out the "name" field on a planet you hard-code into a system, and it SHOULD be named automatically like the other planets;
• you CAN hard-code six stars in the second lane (see below for other problems, but this helps me a lot!); and 
•  you cannot put binaries anywhere but the center lane (nothing shows up), but you can put unary stars anywhere.
• you cannot have more than three planets of any type per lane in the random system generator - this greatly complicates my life. This did not happen before, and I assume it was done to reduce the object count;
• planets will try to be one hex apart,  planets in adjacent rings cannot be adjacent, which means that three in the first ring and three in the second makes an artificial-looking little triangle that looks terrible! I guess they wanted things to look more clear by spacing the planets, but it ends up looking awful! I have now seen one (1) exception to this rule. Otherwise, a 3-3 lane structure always produces what I am calling the "triangle of ugliness."
• The system weights don't work the way one would assume that they do. Two systems with the same star and a weight of 50 do NOT give that star a weight of 100 in the final calculation. Logically, one would assume that the chance of a particular system is = its weight/ the sum of all weights, in which case the weights should be additive. This is clearly not the case: my K class stars have two systems each with a weight of 148, and K stars are not nearly as common as the one G system with a weight of 215, or even the F system with a weight of 157! However, four M systems with a weight of 255 virtually guarantees that nearly all stars will be M, rather than one in four being a G or an F. I suspect that an exponent is involved... See new comments below...

Things that will cause crashes:

• having more than one thing in the central lane causes a crash (pre-Crusade it didn't do this, you could pile stars in the central lane, they would all be in the same hex, and each would get a separate name); This does work... if you use the correct star name... sigh...
• There is a crash if you try to completely fill the second lane of a binary. I forgot how it works, I just remember that it is dangerous; - irrelevant now.
• having too many planets in a lane can apparently crash it (I'm experimenting, definitely fewer than 6*radius+1 (the size of the lane). This may be a crash when min planets = max planets too, I haven't checked yet (it takes a long time to load on my computer). NOTE: pre-Crusade the program used to just make an extra lane for the overflow; and Having trouble confirming this, see below...
• there is another, elusive crash involving multiple stars in an outer lane, but I haven't figured it out yet. Again, a coding issue...
• I am having trouble convincing the system to put more than three random planets in a lane. I cannot explain this. It is very disconcerting... I suspect this may only be a map-generator behavior. If it is, it would seem to be new for Crusade.

Can anyone add anything or correct any of my observations? Some of them are still pre-Crusade, and may have changed. I will try to update this OP as I find new things, or as new things are reported in the comments.

Thanks again to the modding community for being so willing to share their experience. I hope this 'pays it forward' a little bit!