svn：switch不能与相对的svn：external一起使用？

We have a subfolder that is a relative svn external (../project/subfolder). In a fresh trunk checkout it points to (...TRUNK/project/subfolder) and in a fresh branch checkout it points to (...BRANCH/branchName/project/subfolder). But if you do a switch on the project containing the subfolder, the subfolder stays pointing at TRUNK. Alternately if you do a BRANCH checkout and switch to TRUNK it stays pointing at BRANCH. We have a subfolder that is a relative svn exte