cabal-install sometimes gives empty build-log and no build-summary

[igloo]

Building NaturalSort-0.2.1 with GHC 7.0.1 RC 1:

$ cabal install --build-summary=log.bs --build-log=log.bl
Resolving dependencies...
Warning: NaturalSort.cabal: This package requires Cabal version: >=1.6 && <1.9
cabal: Error: some packages failed to install:
NaturalSort-0.2.1 failed during the configure step. The exception was:
user error (The package requires Cabal library version -any && >=1.6 && <1.9
but no suitable version is installed.)
$ cat log.bs
cat: log.bs: No such file or directory
$ cat log.bl
$ 

I would like the build log to contain the error.

I have

$ cabal --version
cabal-install version 0.9.2
using version 1.9.2 of the Cabal library 

but this is not a released version; if nothing else, I have the #697 patch applied.