[MapProxy] Differerence between cached and not cacheed wms source

[shinkarev.alexander at soft.byndyu.ru]

[info] 95.78.166.39 - - [30/Oct/2012 21:43:19] "GET /service?LAYERS=susu_all&TRANSPARENT=TRUE&FORMAT=image%2Fpng&SRS=EPSG%3A900913&SERVICE=WMS&VERSION=1.1.1&REQUEST=GetMap&STYLES=&BBOX=6418264.3901563,7279251.0766406,6496535.9071094,7357522.5935937&WIDTH=256&HEIGHT=256 HTTP/1.1" 200 -
[2012-10-30 21:43:22,128] mapproxy.source.request - INFO - GET http://gis.susu.ac.ru/wms1?styles=&format=image%2Fpng&height=2030&bbox=11486135.5515,6017982.8052,11565123.7456,6163241.51225&transparent=True&layers=F1,F2,F3,F4,F5,F6,F7,F8&service=WMS&width=1104&request=GetMap&srs=EPSG%3A28411&version=1.1.1 502 - 5
[2012-10-30 21:43:22,128] mapproxy.source.wms - WARNING - could not retrieve WMS map: HTTP Error "http://gis.susu.ac.ru/wms1?styles=&format=image%2Fpng&height=2030&bbox=11486135.5515,6017982.8052,11565123.7456,6163241.51225&transparent=True&layers=F1,F2,F3,F4,F5,F6,F7,F8&service=WMS&width=1104&request=GetMap&srs=EPSG%3A28411&version=1.1.1": 502
[info] 95.78.166.39 - - [30/Oct/2012 21:43:22] "GET /service?LAYERS=susu_all&TRANSPARENT=TRUE&FORMAT=image%2Fpng&SRS=EPSG%3A900913&SERVICE=WMS&VERSION=1.1.1&REQUEST=GetMap&STYLES=&BBOX=7044436.5257812,7279251.0766406,7122708.0427344,7357522.5935937&WIDTH=256&HEIGHT=256 HTTP/1.1" 200 -

That kind of log, and a little bit strange thing that when i add zoom level i see just a head of the map after next increasing of zoom level i'll see nothing.