Series automatic ordering (without numbers) fails for new release group

I have created an automatically ordered RG series without number attributes which should be sorted by the earliest release date (according to MBS-7557). This seemed to work fine, but whenever I add a new RG to the series it is inserted into the series at a wrong position (1st screenshot, IIRC the new elements order is always 1).

A simple hack to fix this is to enter the following two edits:

1. Give the new element a (random) number (2nd screenshot).
2. Remove the number attribute (3rd screenshot).

It's annoying to do this every ( ? ) time after adding a new entity, especially as this hack does not work always as it seems (The last fix for the example series took me two attempts).