Impact of alter table on interval partitioned tables

 I have a large 11gR2 database (11.2.0.3) on Oracle Linux (x86-64). This has several large partitioned tables implemented with interval partitioning (no sub partitions).  Sometimes the developers wish to make changes to non-partition key columns (data type or column name).  We use exchange partition to move data from these interval partitioned tables to history tables of the same structure. I find that if I use alter table to make these changes, it seems to a) change what oracle imagines to be the first partition of the interval partition table, and b) seems to prevent partition exchange, as now oracle gives