Global Tempo Automation Failing with VSTs

[OutbackMan]

Bug Summary

Creating a global tempo automation track causes silence and intermittent sounds to be played for VSTs.
Based off discussion from: LMMS Forum Support

Steps to reproduce

1. Download a VST, e.g. Spitefire LABS VSTs
2. Insert a series of notes using the piano roll with this VST. It is easier to hear the effects of the tempo automation if using short repeated notes, e.g 16th notes, however any note length will work.
3. Create a global tempo automation track whose line follows that of a 'mountain', e.g. a curve that goes up and down.

Expected behavior

The tempo of the notes played slowly increases until time reaches the maximum point of the automation curve at which the tempo of the notes slowly decreases. The tempo of the notes played steadies when the automation curve is a flat line.

Actual behavior

The tempo of the notes played slowly increases until time reaches the maximum point of the automation curve at which silence is mostly heard, with intermittent notes played. The tempo of the notes played steadies when the automation curve is a flat line.

Screenshot

LMMS version used

Windows x64 1.2.1

[PhysSong]

Possibly related: #3775

[Spekular]

There's also #5122 and #3640.

[DomClark]

Reproduced. I'm fairly sure this is a duplicate of #5122. I intend to fix that issue soon, and will reopen this issue if that doesn't fix it.