Features rendered with WebGLVectorLayerRenderer disappear when WebGLTile layer is added to the map

[lysek]

Describe the bug
I discovered a bug with a certain combination of GL and non-GL layers (see example below). OL somehow makes the features rendered with experimental WebGLVectorLayerRenderer disappear if you add/remove another GL tile layer to the map, it is needed to pan/zoom the map a little to make them visible again. The bug disappears if you remove the classic vector layer from the map (named vectors in the example - line 59 - it contains the green line). This happens in FF and also in Chrome.

To Reproduce

• I made this fiddle: https://jsfiddle.net/ghx0eb2u/
• Click the "Add or remove GL tile layer" button
• see that the red line disappears when GL tile layer is added/removed

Expected behavior
The red line should be visible all the times.

Use case
I use normal tile layer for background map, WebGL tile for shading, vectors for some features and I wanted to use WebGLVectorLayerRenderer for some special lines with image pattern. The terrain shading layer can be turned on/off and that makes the GL lines invisible.