reconfigure of stacked-on branch does not check stacked repo will be compatible

Reconfiguring a stacked branch to use a shared repo with a different rich-root support seems to break the branch in question. The attached script demonstrates the issue. It would be nice if either things worked or reconfigure would print a suitable error message, maybe asking users to unstack the branch first, and then abort without modifying anything.

+ bzr init --1.6 src
Created a standalone tree (format: 1.6)
+ cd src
+ echo foo > foo
+ bzr add foo
adding foo
+ bzr ci -m foo
Committing to: .../testing/src/
added foo
Committed revision 1.
+ cd ..
+ bzr clone --stacked src dst
Created new stacked branch referring to file://.../testing/src/.
+ bzr info dst
Standalone tree (format: 1.6)
Location:
  branch root: dst

Related branches:
  parent branch: src
     stacked on: src
+ bzr init-repo --2a .
Shared repository with trees (format: 2a)
Location:
  shared repository: .
+ cd dst
+ bzr reconfigure --use-shared
Doing on-the-fly conversion from <RepositoryFormatKnitPack5> to <RepositoryFormat2a>.
This may take some time. Upgrade the repositories to the same format for better performance.

+ bzr info
bzr: ERROR: KnitPackRepository('file://.../testing/src/.bzr/repository/')
is not compatible with
CHKInventoryRepository('file://.../testing/.bzr/repository/')
different rich-root support
+ bzr status
bzr: ERROR: KnitPackRepository('file://.../testing/src/.bzr/repository/')
is not compatible with
CHKInventoryRepository('file://.../testing/.bzr/repository/')
different rich-root support