Cannot download from distributed build working directory

For non-distributed builds, clicking a .tar.gz file on a Working Copy page downloads the file. Clicking on a .zip file shows junk in the text panel, but I can then use the "Download as Text" link to download it. For distributed builds, neither of these operations work.

Specifically, on the Working Copy page of a distributed build:

• Clicking on a text file displays its contents (OK).
• Clicking on a .tar.gz file displays an empty contents panel (for non-distributed builds it downloads directly).
• For ANY file (even text), clicking on the "Download as Text" link replies "The URL requested results in an internal error."