While a sketch is running, selecting File-Save from the menu, or pressing the
corresponding toolbar button, will terminate the sketch. Prior versions (circa <=
0135) performed the save without interrupting run.

this was done to prevent problems with in-use files (it's actually been in
there for a while.. but perhaps it only recently started working properly),
though for a regular "save" it's not so fun, so i think i'll look into
disabling it.