Release 3713 will not build html5

I just ran a bunch of programs I have sitting around. I did manage to trigger this on one of them, otherwise okay. I’m now struggling to pin down the troublesome one again, annoyingly… any chance you could send a tiny example that reproduces it?

We’re merging this stuff, which includes lots of graphics stuff, so WebGL hiccups aren’t totally unexpected. (Would also like to know about any non-web weirdness too, of course.)

Build 3712 is everything up to that point, so fine to use.