plus the light black went down to 14%, all other inks went to halffull.
Unfortunately that's normal, as the printer has to charge the LK ink line twice, once when it charges the MK line, then it swaps to PK and charges that, basically recharging the LK line again.
I always recommend a buyer get a LK cartridge pretty quickly to have on hand because not only does it start out low, it is is the most used ink, often more than all the other inks combined in a print. If opting for the 350ml cartridges, use the 700ml for LK. LLK is also used quite a bit, some also run the 700ml in that as well.