This is a problem and will take some careful doing. Using the herbicide roundup, Carefully paint the leaves of the weeds. This herbicide will kill or damage any plant it touches, so take care not to drip it on the ground cover. The weeds should die in 10 days. If they are persistant you may have to do it again in spring. Best Nancy.
Getting rid of the weeds is fiddly work. Keep painting those weed leaves. Once the bed is clean, using Preen will help keep new weeds from sprouting. But if you disturb the soil the Preen must be reapplied. Happy Yardening, Nancy