I'm using ArcGIS (Desktop 10.2.2) and I have some graphic lines drawn over my data which I wish to modify. When I click on one with the Select Elements tool the line is selected (handles appear) but the Edit Vertices button on the Drawing toolbar remains greyed out. I also cannot move them (Select Elements cursor never changes to the cross-arrow when I mouse over the line), or delete or group them (those options in the context menu are greyed out).
It seems to be replicable in that if I create a new line (or copy and paste an old one) I can edit it, but if I close and reopen the map document the 'new' line then shows the same problem and cannot be edited. It's as if a save + close somehow "locks" the graphic.
What has happened to my graphic features to make them non-modifiable?