Here is an example of how a simple misunderstanding in the rules can break a game.
My 1982 game Dragon Rage was reissued at the beginning of 2011. The process of finding a publisher, who was a new publisher, and getting the game arranged and printed took about three years. The publisher, Eric Hanuise of Flatlined Games, felt he should rewrite the rules in a more modern style, more sequence of play than the old rules which were written in a reference style as most were in the early 1980s.
At one point he told me that the dragons seemed to be losing an awful lot of games in his playtesting with the newly written rules and asked me if I could figure it out. So I took his preliminary art and mounted the board and pieces on foam board and painstakingly cut the pieces out. Then I took it up to my brother's house (more than 300 miles-- but he had experience of having played the original version). I sat in his living room with my originally submitted rules, the originally published rules, and Eric's version of the rules and tried to make comparisons.
Fortunately it didn't take long before I got an idea of what had happened. Corresponding with Eric confirmed it. In Dragon Rage the defenders get reinforcements by ship after the game has been going for a while and at regular intervals thereafter. The design purpose was to force the dragons to have a go rather than hang back and fool around. If the dragons simply charge in and blunder about, they'll likely be killed. So the dragons have to pick and choose their times and places to act, sometimes nipping in and out, and the reinforcements help induce them to actually attack rather than fool about. In other words, the reinforcements provide the momentum toward a conclusion, something every game must have, as what starts out with a slight advantage to the dragons gradually becomes an advantage to the defenders.
The timing is determined by turns. And Eric had counted turns differently than we did in the old days (and, I suspect still do in wargaming). In the old days, play by one player and then the other constituted a single turn. Eric counted this as *two* turns. So the reinforcements started coming after five turns rather than 10 turns, and thereafter came twice as fast (every two turns instead of four). Keep in mind that Eric's native language is the Belgian version of French, not English, so this misunderstanding is not surprising. But it made a huge difference in how the game played.
This illustrates why the designer ought to be involved in the production of the game. Often, once the designer submits the game, he has virtually no input in production.
While we're on the topic of Dragon Rage, it is notable because the maps, which have a lot of detail on the two-sided mapboard, were not drawn by a professional artist. Campaign Cartographer 3 by ProFantasy is a fantasy map-making program built on top of the FastCad computer aided design program. It is powerful enough that Eric Hanuise of Flatlined Games was able to use it and CityDesigner3 for the maps, thus trading his time to learn the program in order to save very substantial artist fees (no licensing fee from ProFantasy required). See http://www.profantasy.com/rpgmaps/?p=571 for a brief description with the final maps. The step-by-step process is described at http://www.profantasy.com/rpgmaps/?s=Dragon+Rage (scroll down to September 12, 2011).