I've noticed that RCS jump out of the tank if there is any ammonia or nitrite in the water. I'd check those levels. Also, if oxygen levels are low fish will try to breathe water at the surface because there is more oxygen there. So maybe that's what they're trying to do?
edit: I just noticed you said it was a fish and plant tank. If your friend uses fertilizers or CO2, the shrimp could very well be trying to escape those conditions. It sounds like they're trying to get out, probably due to that and the fish
In all my tanks that have Cherrys they inhabit every area, substrate, middle, top. My tanks are all variously planted, but I use floating plants, mostly Salvinia, which the shrimp enjoy hanging upside down on picking away. I have certainly never seen them "on" the surface however.
CO2 and fertilizers will not drive a shrimp from the tank unless they are at toxic levels, and even then I would suspect they would not attempt escape unless they were capable and/or aware that was an option. Lack of oxygen in the water column, however, will drive fish to the surface, not sure about inverts.
When water conditions are bad the shrimp will stand on floating plants and even jump out of the tank. I've seen this when I was first starting with shrimps and was using a phosphate based buffer.
