Switching from continuous to pulse to continuous creates a wave.

[KatieWoe]

Test device:
Dell Laptop
Operating System:
Win 10
Browser:
Chrome
Problem description:
For phetsims/qa#238. May be related to #144.
Under certain circumstances the water scene will create an unprompted wave when switching from pulse to continuous. I have not reproduced with sound or light. It may be easier with a frequency change, but it is not necessary. This occurs in both side and top view.
Steps to reproduce:

1. Go to the wave screen and make sure water is selected
2. Turn on a continuous wave
3. While that wave is still occurring, switch to pulse. This shuts off the wave
4. Before the original wave has left the view area, switch back to continuous, this creates a new wave

Screenshots:

https://drive.google.com/file/d/1Q5qcDst8mfqhLN3Focyj-fNH6Lz1E4eh/view?usp=sharing

Troubleshooting information (do not edit):

Name: ‪Wave Interference‬
URL: https://phet-dev.colorado.edu/html/wave-interference/1.0.0-dev.51/phet/wave-interference_en_phet.html
Version: 1.0.0-dev.51 2018-12-12 03:47:24 UTC
Features missing: touch
Flags: pixelRatioScaling
User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.80 Safari/537.36
Language: en-US
Window: 1536x732
Pixel Ratio: 2.5/1
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: 30 uniform: 4096
Texture: size: 16384 imageUnits: 16 (vertex: 16, combined: 32)
Max viewport: 16384x16384
OES_texture_float: true
Dependencies JSON: {"assert":{"sha":"928741cf","branch":"master"},"axon":{"sha":"73e761ec","branch":"master"},"brand":{"sha":"1fd6682e","branch":"master"},"chipper":{"sha":"61bc739b","branch":"master"},"dot":{"sha":"b45eafe8","branch":"master"},"griddle":{"sha":"914c9215","branch":"master"},"joist":{"sha":"5a013a46","branch":"master"},"kite":{"sha":"f3e96e5b","branch":"master"},"phet-core":{"sha":"86dec8cc","branch":"master"},"phet-io":{"sha":"a267fdb1","branch":"master"},"phet-io-wrapper-classroom-activity":{"sha":"5dea7f54","branch":"master"},"phet-io-wrapper-hookes-law-energy":{"sha":"b42eaef7","branch":"master"},"phet-io-wrapper-lab-book":{"sha":"b884e9c1","branch":"master"},"phet-io-wrappers":{"sha":"d5b42848","branch":"master"},"phetcommon":{"sha":"869b2561","branch":"master"},"query-string-machine":{"sha":"e4f9e8e8","branch":"master"},"scenery":{"sha":"a18ce7f1","branch":"master"},"scenery-phet":{"sha":"56df5b6d","branch":"master"},"sherpa":{"sha":"a1f5e867","branch":"master"},"sun":{"sha":"38ed71af","branch":"master"},"tambo":{"sha":"746fbd32","branch":"master"},"tandem":{"sha":"c7a56e2e","branch":"master"},"twixt":{"sha":"e38c70ed","branch":"master"},"wave-interference":{"sha":"bfce593d","branch":"master"}}

[arouinfar]

Nice find @KatieWoe.

@samreid here's a screen capture showing the top view.

[samreid]

Proposed fix pushed to master, @KatieWoe can you please review on phettest and close if all is well?

I also noticed a potentially related problem, I'll create a new issue for it.

[KatieWoe]

Looks good in master