"Save Failed" while editing accounts that have been created with capital letters in their username

[garned]

I have only experienced this issue with accounts that have capital letters in their username and the error message seems to support this observation.

I can create the account 'FooBar' without any issues.

But if I want to edit it, it displays the following error message:
Save Failed: Flex saveFile(foobar): Flex moveFolder(account:///FooBar, account:///foobar): Cannot move non-existing folder.

Trying the same for an account called 'foobar' works fine