Underneath the Display panel are a few miscellaneous options you can select between when editing meshes.
Edge Extend 0/1/10
Select the look-ahead range for cut'n'weld operations. Click on the Edge Extend button itself to unselect all red or yellow highlighted edges.
Auto Fit/Off
When Auto Fit is on, all current UVs are re-normalized (scaled to fit in the 0 to 1 range) every time a UV shell is moved or modified. When Off, they aren't, so you can move shells beyond this range and out onto other tiles. Use the + and _ keys to scale the UV unit box up and down.
O/C/N
When O is selected the original (pre-v1.9) flattening algorithm is used for all flattening calculations. When C is selected, the current most reliable method is used. When N is selected, a newer method is used that handles long thin polys better, but its very new, so the older methods are still available if the new method fails for some reason.
