Q: Infinite length lines coming off polygons in shapefile I have been sent some OS MasterMap topography area shapefiles. (OS MasterMap is a national map product including pretty much every permanent structure and land parcel.) 
A few of the polygons in each of them have what appear to be lines of infinite length attached to them. 
The layers use the British National Grid CRS (EPSG 27700); the lines stretch back to the zero x and y coordinates in the west and south, but carry on infinitely to the north and east.
The three layers in question:

Context of lines against UK:

The lines are not selectable using select feature, and they disappear upon zooming in. GRASS GIS v.clean remove dangles tool removes the vertical ones, but not the horizontal ones. 
As they are not selectable, I cannot identify the affected polygons to manually correct them.
I am using QGIS 2.18.0. This problem also occurs on my colleague's PC, with ArcGIS 10. On ArcGIS, the layers cause errors when attempting to get summaries or similar. On QGIS, the summary algorithms simply fail to complete.
What is the cause of these lines and how can I fix them?
