If you were using the XS Stash, I don't think this would be a problem.
If you really have a reason to use the non-XS stash, you can patch TT. The fix is to change the code that creates the $atroot variable in the _dotop method. It is described in this post to the TT mailing list. There is similar code in _assign that could probably stand to be patched as well.
Note: The change in question adds a dependency on the Scalar::Util module, which should work on whatever version of Perl you can run TT on.