EDIT: This apparently is a bug (https://developer.blender.org/T52723)

However, I'm still creating bmeshes in the draw method of my panels which is bad practice, but not the cause of this problem.

I've been developing an add-on for Re-Volt file types for a while.

I'm not sure if I discovered a bug or if I'm doing something wrong: As soon as I call bm.faces.layers.int.new("LayerName"), the UV Unwrap Reset operator starts behaving weirdly.

Usually, when you reset the UV on a cube, you get the faces mapped as squares. After creating a new int layer on the bmesh, it starts mapping faces to lines or other weird shapes that sometimes go beyond the UV bounds.

example uv image

I create those int layers to store flags for each face. The layers are created upon import and in Edit mode. I made a tool panel for setting those flags. It all works fine, it just breaks the bpy.ops.uv.reset() operator.

Launching Blender with --debug-all also didn't reveal any interesting details. Everything in the logs looks like it's supposed to.

I also tried opening the Blender files with that problem in older and newer versions than 2.78 and the problem persists there, it seems to be in the mesh.

Here's a .blend with the problem: http://pasteall.org/blend/index.php?id=47471

Here's the wider context of creating a new int layer (panel in the 3D view):

class RevoltFacePropertiesPanel(bpy.types.Panel):
    bl_label = "Face Properties"
    bl_space_type = "VIEW_3D"
    bl_region_type = "TOOLS"
    bl_context = "mesh_edit"
    bl_category = "Re-Volt"

    selection = None
    selected_face_count = None

    def poll(self, context):
        return (context.object is not None)

    def draw(self, context):
        obj = context.object
        mesh = obj.data
        bm = bmesh.from_edit_mesh(mesh)
        flags = bm.faces.layers.int.get("RVFlags") or bm.faces.layers.int.new("RVFlags")
        texture = bm.faces.layers.int.get("RVTexture") or bm.faces.layers.int.new("RVTexture")

Here's the section on GitHub if that helps: https://github.com/Dummiesman/HabitatB/blob/dev/io_scene_habitatb/panels.py#L104

Please tell me if I could provide more information. I'd be really thankful if someone has an idea.

  • 1
    $\begingroup$ Changing ID data in a panel's draw method is a NO NO. (will throw an error for obj.location = (0, 0, 0) for example). The draw method runs many times (esp if mouse is over), put in a print statement to check. You will be making multiple instances of bmesh.from_edit_mesh() Have a look at on how to make a global dic and use one edit mode bmesh for the panel. $\endgroup$
    – batFINGER
    Commented Aug 15, 2017 at 12:24

1 Answer 1


This is a Blender bug. It has been fixed: developer.blender.org


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