Extra vibration in string when switching to No End

[arouinfar]

Test device: MacBook Pro
Operating System: OSX 10.9.4
Browser: Chrome 37.0.2062.120

Problem description:
When switching from a fixed or loose end to no end, there is an additional vibration that propagates towards the source of the wave, reflects, and then goes out the window. This behavior is easiest to see in slow motion, but is also visible at the normal playback speed. I have been able to produce this extra vibration while using all combinations of manual/oscillate/pulse with fixed/loose end before switching to no end. The extra vibration only shows up if the string near the end is displaced from the midline while switching to the window.

Steps to reproduce:

1. Choose pulse, fixed end, and slow motion (easiest combination to see the issue)
2. Click on the pulse button once and let the wave propagate toward the clamp.
3. When the wave reaches the clamp, pause the sim and switch to No End.
4. Unpause once the window is on screen. The extra vibration should be visible.

Severity:
This behavior has been noticed by a student in an interview and does have the potential to interfere with learning, so it should be fixed before the sim launches.

Screenshots:

Troubleshooting information (do not edit):
Name: Wave on a String
URL: file:///Users/rouinfar/Desktop/wave-on-a-string_en.html
Version: 0.0.0-dev.15
Features missing: touch
Flags: pixelRatioScaling
User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/37.0.2062.120 Safari/537.36
Language: en-US
Window: 1312x683
Pixel Ratio: 2/1
WebGL: WebGL 1.0 (OpenGL ES 2.0 Chromium)
GLSL: WebGL GLSL ES 1.0 (OpenGL ES GLSL ES 1.0 Chromium)
Vendor: WebKit (WebKit WebGL)
Vertex: attribs: 16 varying: 31 uniform: 1024
Texture: size: 16384 imageUnits: 16 (vertex: 16, combined: 16)
Max viewport: 16384x16384
OES_texture_float: true

[jonathanolson]

Also present in the old Flash sim.

[ariel-phet]

@jonathanolson I don't think this is a blocking issue, but it should be fixed at some point. Lets get everything else done and see where we are at.