Red triangle remains in numberfield after store sync

Has anyone else noticed that the red triangle remains in a numberfield cell in a grid even after a successful store.sync()?

The sync() definitely is successful; if I refresh the grid afterwards the triangle goes (and the value in the cell remains the same, obviously). I'm using 5.1.0.107. Problem seems evident in Chrome 40 and IE 11 so far.

This only seems to be when editing an existing record (I'm using it with a REST proxy, so POSTs are fine, but PUTs don't remove the red triangle).

Red triangle remains in numberfield after store sync