There seems to be a bug there.

In game #1830710, I wish to capture the centre, making it a 4, then white-colour the 5 next to it,

and finally play my own 6 in line with that, all going north-east.

The machine lets me play all this, but refuses to admit that my turn may be finished.

Presumably because it thinks the centre wants to be a 5, and can't change it.

Can someone tell the powers that be that this seems to be a bug, and hopefully get it fixed.

Thanks for any help, kiwibill.

Do you mean, you wanted to play that on the tenth move?

Of course you can consider the asterisk as 4 and then continue with 5, 6 as you wished. The problem is, turning the asterisk into white won't break your opponent connection. You have to find a move that breaks his connection.