--- a/net/server_event.lua	Tue Apr 19 17:10:42 2016 +0200
+++ b/net/server_event.lua	Tue Apr 19 17:32:22 2016 +0200
@@ -521,6 +521,10 @@
 				elseif interface.eventreadtimeout then
 					return EV_WRITE, EV_TIMEOUT
 				end
+				if interface.writebuffer ~= 0 then
+					-- data possibly written from ondrain
+					return EV_WRITE, cfg.WRITE_TIMEOUT
+				end
 				interface.eventwrite = nil
 				return -1
 			elseif byte and (err == "timeout" or err == "wantwrite") then  -- want write again