Leaflet.markercluster: Doesn't support negative zoom levels (Cluster icons don't show up/disappears)

Hi,

I am using an imageOverlay map for my indoor floorplan project with bounds set to the image exact resolution. In the example below it is 2003px*1203px, but it can be higher. I encountered following issues:

1. The cluster icon doesn’t show up when the map is loaded.
2. The cluster icon and the non-clustered marker icon can disappear and show up after zooming (mostly on low zoom levels).
3. The icon’s positioning on the map is not correct at some zoom levels (mostly low zoom).
4. After “playing” with zoom for some time a second cluster icon can appear so you can see 2 clusters for the same markers. Though this happens very rarely and i couldn’t reproduce this issue intentionally.

If i change the bounds from var bounds = [[0,0], [1203, 2003]] to smaller values like var bounds = [[0,0], [120.3, 200.3]] all seem to be working correctly. But i would like to keep the big bounds for my project…

Please take a look at the example: https://jsfiddle.net/8voh7rLs/ For this example i used Leaflet 1.0.0-beta.2 and Markercluster 1.0.0-rc.1.0

Thanks!