qgis - Shape layer turns non-editable if saved filtered

I am working in QGIS 2.18.3.

I have a shape layer with point geometry, which I filter by some field, and then I work on its attribute table. Once I am done for the day, I save the project so I can continue the next day.

I store data on my computer, where nobody else connects to it, I do close the project afterwards, and finally I do switch off my computer.

Here is my shapefile with no filter (can be edited),

then my shapefile after I applied the filter (still can be edited).

But every day, when I open the project, I find the shapefile can not be edited, so I have to un-filter it and then save it with another name, delete de previous one and keep on working on the new one which allows me now to keep on editing.

I have tried duplicating the layer, but the duplicate is still non-editable.

Why does this happen? Is it a consequence of saving the project with a filtered shapefile?