Adding new fields to shapefile alters appearance of borders in QGIS?

Question

I am using QGIS 2.6.0-Brighton and I am trying to add a custom field to my layer made from a shapefile of Italian provinces; everything seems fine when I create a categorized views using region codes, something like this:

then when I try to add a custom field to the associated table in order to create a custom aggregation (like the Macro Region shown on this picture)

when I go back to the map everything seems to be screwed up, and this is the result I am getting (e.g. islands look like little red crosses, thick polygon borders):

Am I doing something wrong or is it a bug?

Answer 1

It is because you are still in editing mode. What you are seeing are little red 'x' symbols over every vertex in your shapefile.

Once you have finished with your edit, right-click your layer and click 'stop editing' and everything will be as it was.

Answer 2

You are in edit mode. Just click the pencil to save your new column and disable edit mode.