Aggregate series - difference to first/last does not show first day of month


using OH3.4.4 I would like to visualize the difference of a continuous graph (more precise the kWh reading of my power-meter).

an aggregate-series does the job pretty good, except that the first day of a month (or first month of year… depending on the setting) is not shown. I guess the issue is, that the aggregate series is just taking this time-period into account and ignoring the last month.

Is this a known issue? Is there any workaround?
I mean I could create a new item and just calculate the daily difference with an rule but that a lot of workaround for a little bug.

This is fixed (at least the diff_last) in OH 4.