Guatelitzi's Abletion support not giving power charges properly

The lineage support gem Guatelitzi's Abletion states that "Offerings from supported skills grant you a power charge every 4 seconds". However, the support only gives the first charge and stops granting additional charges even when the offering is still active.

My current offering skill has a duration of 10.47 seconds, so in theory it should grant power charges twice during the effect, but I only get 1.