2.6.21 Update for hot fix.

2.6.21 update is available now. The changes are as follows.

Now Preference window has unwrap parameters to let you adjust Pack Margin, Hard Angle, Area Error and Angle Error used when generating UV2 to avoid UV2 overlapping.

It was reported that lightmaps got broken every time [Don't Save on Build] was changed in local settings due to unnecessary mesh building. This bug has been fixed in this update.