This case brings to light multiple problems that were introduced by the
[UPDATE-FROM enhancement][1] and [query flattening of UNION ALL][2].
All are now fixed on trunk.
[1]: src:/timeline?c=88baf1eb07065032
[2]: src:/timeline?c=df1d6482f9e92daf
Preconditions to this bug:
1. You must be trying to do an UPDATE-FROM on virtual table that has a rowid.
2. The FROM clause of the UPDATE must contain a CTE or VIEW or subquery that
uses a UNION ALL operator and that is subject to processing by the
query flattener.
3. The UPDATE must contain a vector assignment in which the very first
term on the left-hand side of the assignment is repeated and in which
the right-hand side is a SELECT statement.