renderTexture is cleared when applied to ColorMapFilter

[codemonkeynorth]

call to texture.source.update(); in the filter seems to be causing the render texture to clear to black

the filter works fine when using a canvas based texture instead,

example: https://www.pixiplayground.com/#/edit/zFDEytsuMRpXGCbejFGSR

potentially an issue with RenderTexture itself rather than the filter?

thanks
J