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:

![Italian provinces colored by region code](https://i.stack.imgur.com/UcUr4.png)

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)

![adding the MacroReg field](https://i.stack.imgur.com/4eiii.png)

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):

![screwed up map](https://i.stack.imgur.com/9Uck2.png)

Am I doing something wrong or is it a bug?

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