could you try to add --difficulty-multiplier 2 (I used here a difficulty adjustment of 256).
However what is strange is that on the pool I tried (verter and supernova), I didn't see that at all.
share above target are not submitted (or are not counted as rejected)
Thx, --difficulty-multiplier 2 works like a charm on coinotron, didn't make any differance on verters though.