[ubuntu] Audacity 2.0.5 / 64-bit Ubuntu 14.04: WAV file incomplete read

This has cropped up in the last two weeks.

When I load a 30+ minute stereo WAV file, the first 25 minutes look and sound OK: thereafter the waveform has a complicated but repeating patte. Playing this part of the file results in no output.

If I delete a few seconds from the begiing of the file, I lose more audio from one track than the other.

I have tried three different files, all are treated the same.

It works ok on my 32-bit dektop.

Any clues? Has there been a recent update that might affect Audacity/

Andrew