I know we've already talked about this bug, but I just noticed that you'd cross-posted it to the InDesignSecrets forum. So to close this out as well I'll repost my earlier email response to you.

We have identified what we believe to be a bug in Adobe InDesign whereby it has a fatal crash with a null pointer exception when:

1. you insert a specific number of columns into a table; and
2. the table insertion point intersects with a merged cell (row).

The specific scenario is inserting a number of columns greater than the count of existing columns opposite of the insertion point (side). For example: in a 4-column table if you select column 3 to insert 1 column to the left, the insertion is successful. But if you instead insert more than 1 column to the left, InDesign crashes. Alternately, if you inserted 2 columns to the right, the insertion is successful. But if you instead insert more than 2 columns to the right, InDesign crashes.

We are tracking this internally as bug 4819, but we believe this to be a failure within Adobe InDesign—the exception/crash occurs when AutoFit calls the method GetFrameIndexContaining(theTextPosition) on the existing InDesign interface IFrameList. We are also investigating whether we can access the underlying frame information via alternate methods that do not result in a fatal null pointer exception.

As a workaround, please temporarily disable AutoFit via the Preferences → Typefi → AutoFit Preferences when adding/inserting columns within tables with merged columns (note: this bug affects any table, not just tables within an AutoFit-enabled text frame).