Is it just me, or is I2C1 on pins B8+B9 not working in v71?

I'm having problems with I2C1 on pins B8/B9 on v71.

Is this a general problem, or have I done something bad to my Espruino?

Testing with known working AT24:

>I2C1.setup({sda:b7,scl:b6});
=undefined
>I2C1.writeTo(0x50,[0,0]); //Works fine
=undefined
>I2C1.setup({sda:b9,scl:b8}); //at this point, I moved the wires over to B8/9
=undefined
>I2C1.writeTo(0x50,[0,0]); //now it doesn't work
=undefined
Uncaught InternalError: Timeout on I2C Write Transmit Mode 2
 at line 1 col 24
I2C1.writeTo(0x50,[0,0]);
                        ^
>I2C1.setup({sda:b7,scl:b6}); //Moved the wires back
=undefined
>I2C1.writeTo(0x50,[0,0]); // and it works again
=undefined

Actually, what the heck is going on? I2C2 was working, but now I can't get it to work at all, with any of multiple devices that were working until at least very recently... And downgrading doesn't fix it... I2C1 on B6 and B7 seems to work reliably though..

It may have started when I installed an external crystal, but I removed that, and it's still not working, though it has worked a few times.

Any thoughts? I'm starting to question my own sanity here.