Clipping mask problem: When I make a clipping mask for a map, the fill on the road signs gets removed.

The road signs are not compound paths, just normal shapes. I tried grouping them and making the clipping mask a compound path -- no change. It looks like the signs are behind the roads, but if you look closely you can see that the fills have been removed when the mask was applied. I’ve tried every suggestion I could find, but no difference. Everything else in the map gets clipped correctly; it’s just the signs that get changed. Any ideas?