ZynAddSubFX preview of presets sounds different after clicking other preset

**Steps to reproduce:**
Open fresh instance of LMMS (I used LMMS 1.2.0-rc5.67 on Ubuntu 16.04)
Click on presets:
1. ZynAddSubFX > Bass > 0001-Bass 1.xiz
2. TripleOscillator > SEGuitar.xpf
3. ZynAddSubFX > Bass > 0001-Bass 1.xiz (same as step 1)

**Actual result:**
Step 3 sounds very different from step 1 even though it's the same preset. (Lots of echo and distortion is now added. It sounds as if the effects from TripleOscillator's SEGuitar.xpf affected the sound of ZynAddSubFX)

**Expected result:**
Presets should sound the same every time regardless of what is done in between

Reproduce the sequence using the ZynAddSubFX and TripleOscillator preset preview paths, starting with the listed Bass and SEGuitar presets. Compare the first and third ZynAddSubFX previews and trace how preset or effect state is retained between selections; done means the same preset sounds identical before and after previewing another preset.

Written by the indexing model from the issue text.