Well, I've done a bit of research and I've found one problem in networkSettings.php
Locate the line that contains: if(isset($_POST['swap'])){
The two lines that follow assume that the zero-th entry in the External and Internal Interfaces Array contain either the string "eth0" or "eth1".
If either string is "wlan0", say, then the FALSE option is taken in the subsequent assignment and the interface designation is set as "eth1". This is a bit unfortunate since it is conceivable that both interfaces could be set to "eth1" in which case subsequent SWAP commands will merrily toggle both designations between "eth0" and "eth1". It might be better if the code did not make rash assumptions.
What it doesn't explain is why my "wlan0" isn't automatically set to "eth1" the first time I used the SWAP i/f option. - hmm.
BTW: I took advice and installed the DVD version LMCE having made sure I had a compliant network and found everything worked like it says on the box.