It is so rare that it is worth noticing it.
I wanted to reorganize my Navigation pane and I moved (tried to move) three folders from the Navigation pane, then Xojo 2015r1 crashed n my El Capitan SSD.
Nota: I already moved those folders from their disk location into another folder; all images files in a single location on disk.
I will do the same for some other “support“ files.