Hi. I have built version 66 one hundred times in unstable. The builds were made on 19 different autobuilders. The number of failed builds has been zero. (Previously it failed 10% of the time).
If you do not remember what kind of change may have fixed this, then there must be some broken build-depends in testing which is fixed in unstable. I guess the right thing to do would be to find which one, reassign this bug, and then close it, but we should ensure that the fixed build-dependency propagates to testing. Thanks.