You're saying that the setting in WPtouch will not save. You'll want to test your WordPress installation for conflicts.
To isolate which plugin(s) may be contributing to the trouble, deactivate all except WPtouch from within the WordPress Plugins area, clear your browser cache and local data then test.
If WPtouch functions well, you may then enable the rest of your plugins one at a time, repeating the process, until you can identify which is/are causing the problem.
You may choose to replace the conflicting plugin with another or upgrade to WPtouch Pro which has a feature that will allow you to disable the conflicting plugin within your mobile theme but leave your desktop theme intact.