Why gradient color failed? LVGL 8.4

General discussion
1

With only on gradient color button.
lv_obj_set_style_bg_grad_color(ui_CAM_ON, lv_color_hex(0xD6E9C4), LV_PART_MAIN | LV_STATE_DEFAULT);
lv_obj_set_style_bg_grad_dir(ui_CAM_ON, LV_GRAD_DIR_HOR, LV_PART_MAIN | LV_STATE_DEFAULT);

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With two gradient color buttons.
lv_obj_set_style_bg_grad_color(ui_CAM_ON, lv_color_hex(0xD6E9C4), LV_PART_MAIN | LV_STATE_DEFAULT);
lv_obj_set_style_bg_grad_dir(ui_CAM_ON, LV_GRAD_DIR_HOR, LV_PART_MAIN | LV_STATE_DEFAULT);
lv_obj_set_style_bg_grad_color(ui_CAM_OFF, lv_color_hex(0xD6E9C4), LV_PART_MAIN | LV_STATE_DEFAULT);
lv_obj_set_style_bg_grad_dir(ui_CAM_OFF, LV_GRAD_DIR_HOR, LV_PART_MAIN | LV_STATE_DEFAULT);

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Is this a bug? Or do i did something wrong?

Thanks,