I just recently had two lockups. (Un)Fortunately neither one was reproducible.
Both involved tables: I was creating a calendar.

1. Actually a runaway memory leak. When there was no memory or swap left the
kernel killed the culprit: PageStream. What I had done was create a new
document and setup the table (8 columns by 5 rows) and sized it to the page.
The top row didn't need to be as large as the others, so I knocked it down to
16 points, IIRC. PgS either quit responding after doing that, or when I tried
to resize the table.

2. Same document, just much farther along. One page for each month (12) and on
page 6. I was putting in moon phases (using a font for that purpose). The
table had been duplicated to every page and I was just selecting the moon
phase character and typing the correct one. This time it somehow got after
the moon phase character and put in the character in the normal text font. I
hit ctrl-z to undo it and PgS quit responding. Eventually had to kill the
process.

I suspect in the second case that PgS had managed to do something it shouldn't
and hence the undo tried to undo something it couldn't. I can't get either
one to replicate.

Tim Doty