Hi,
just to let you know I got some stable examples running using this example wifishield/SimpleWebServerWiFi.ino at hd_2.7 · arduino/wifishield · GitHub
I still don't know why it is reliably working anyway. I also must admit I don't drive any motor with it now.
Of course this may constrain the architecture of the solution you're planning to build.
I keep you posted on this.
Best regards,
Benoît