You are probably right, the transmission is summed but the density matrix is only for the last calculation.
Once should not expect the sum of all parts to always be exactly 100% (sometimes it's even above) because it is very difficult to time exactly each part. The report is only meant to give a general idea about where the bottlenecks in the calculation are, this can help determine whether it would make sense to parallelize this job on more nodes, for instance.
However, the discrepancy should not be as large as that you observe, then it becomes useless. The reason is, as you have guessed basically, that the functionality for timing is intended for the case when you have one calculation in the script.
We'll have a look at how we can improve this functionality for more general cases.