[Audacity-quality] All Nyquist effects fail with part of this project

[Steve t. F. <ste...@gm...>]

Test project: https://www.sendspace.com/file/71n8cr

This bug occurs with Audacity 2.1.3 built on Nov 23rd, on Linux (Debian Xfce).
I've not yet tested with a later build or any other platform, but I'm
raising it on list as it may be very serious given the planned
release.

Apply any Nyquist effect to (about) the first 1000 samples of the
second audio clip in the linked project.

Requirement for the problem to show:
1) The selection starts at the first sample of the second audio clip.
2) The selection is less than 1921 samples duration.

Result: the selected audio disappears.

Very simple test script:
This scrip should return the selected audio totally unchanged.

;codetype lisp
;version 4
*track*


So far I've no idea why this is happening, and that is very worrying
as permanent data loss is occurring for reason unknown.

Steve