Waveform Editor Bug

When editing in the Waveform window, once I delete the content of an audio file - the waveform itself is still visually showing in the edit window. But the actual audio content is no longer there. It will not erase visually when I click delete (or CTRL-X). The only way to remove the visual representation of the waveform is to hit record again, which then returns the edit window to black. This has only just started happening since the last update.