It seems glibc's extrapolation of existing DST-rules cuts off at some point in the distant future, where the IANA DB gives no end-time for such rules, leading QTimeZone to keep applying them. This lead to tst_QDateTime::fromSecsSinceEpoch() not getting an invalid date in one of its bounds-probing tests, due to a within-bounds datetime getting glibc's offset and then the out-of-bounds one falling back to the IANA rule's offset that put it back within the bounds. This directly affected Australasian zones (which glibc locks into daylight-saving time in this distant future) which were fixed by using the IANA DB's offset; but the relevant date is in August so other zones, north of the equator, that glibc locks into standard time, then had the reverse problem, so we have to take the minimum of the two sources' offsets to get all zones on board. Change-Id: I0c94af2ba108dea31bee46aafa4a8cca8d373a5c Reviewed-by: Thiago Macieira <thiago.macieira@intel.com> Reviewed-by: Konrad Kujawa <konrad.kujawa@qt.io> Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>