Hi,
I don't think it's completely because of builder issue. If it is an issue in builders wouldn't all the packages in experimental be built with 5.6.0?
Some of the packages in experimental are built with 5.5.1 and some are built with 5.6.0.
examples:
built with qt 5.5.1: bluez-qt, karchive
built with qt 5.6.0: kwidgetsaddons, kcodecs, kconfig
I can't see directly from the build dependencies what would make the builders choose 5.6.0 for some and 5.5.1 for some.
karchive
Build-Depends: cmake (>= 2.8.12),
debhelper (>= 9),
extra-cmake-modules (>= 5.19.0~),
libbz2-dev,
liblzma-dev,
pkg-kde-tools (>= 0.15.16~),
qtbase5-dev (>= 5.4),
zlib1g-dev
kconfig
Build-Depends: cmake (>= 2.8.12),
debhelper (>= 9),
extra-cmake-modules (>= 5.19.0~),
pkg-kde-tools (>= 0.15.15ubuntu1~),
qtbase5-dev (>= 5.4),
qttools5-dev (>= 5.4),
qttools5-dev-tools (>= 5.4)