The InsertGroup will not group operations starting with (and including) its _doNotGroupBeforePoint iterator, which is set to the last operation grouped in the last attempt, or the start of its operation vector. This means it can never group the first operation in the operation vector. Since there is no "before the beginning" iterator in C++, probably the solution is to make _doNotGroupBeforePoint the first operation not yet grouped, and make InsertGroup not group operations strictly before _doNotGroupBeforePoint.