After unwrapping a cylinder-type of object (seams marked) I get three islands (top/bottom/side). No distortion, works as expected.
BUT: As soon as I select one island (using the island selection tool, but it's the same problem with manual selection) and press "S" or "G" the uv mesh gets strangly distorted (some vertices are merged, distances between vertices change). The distortion starts before I even actually move the mouse.
EVEN STRANGER: When I append the object into a new blender file, everything works just normal!
So I opened the original file and in another blender session the new file in which I appended the object to. I've compared the UV editing screens trying to find any difference (snapping turned on/off, proportional editing on/off, local/global settings, etc.). I could not find anything!
I think there must be any function turned on causing this strange behaviour, but I can't find it.
I've also tried: - Closing/Re-Opening Blender using original file - Re-Save original file - Save original file giving it another name - I even restarted my pc...