Cracks: When there are lots of varibles, trying to isolate a single cause is very hard to do, especially from people outside the shop where it occurred. Picts do help sometimes.
Sometimes causes: Cold as in NY
humidity and cold
green wood, or humidity swings
Accelerant in conjunction with any of the above.
The problem with any of these and accelerant is that 6 or 7 of 10 will have no problem. And those with no problem will assume that it is not the accelerant when it could be - that said because Accelerant CAN cause or be a catalyst for cracks. While accelerant works most of the time, it is a varible that has to be factored in with the others.
For me, I know how to use it and I use it sparingly. Keeping finishes simple cut a lot of variables out, and it also makes the finish more predicitable. The two or three minutes accelerant saves is not worth it over the long run for me. I have made pens on two continents, in hot and humid and cold and dry as well as cold and humid.
Humidity swings will cause some woods to move;
CA inside the tubes and then mounted can cause cracks. Most of the time it will happen when pen parts are pressed together, but sometimes it doesn't happen until a few days after putting the pen together.
There have been a couple of times when people have asked about what seemed to be cracks only to find out that it was the grain and the way it showed through the CA.
If you can, post some picts.