Has a bug

I just tried your latest SSP3 program.

I instinctively tried to navigate using the cursor keys, but only the Tab and Shift-Tab keys worked. You should try to get it to work with the cursor keys.

I mistakenly entered the number 2 in the wrong box and pressed Delete to remove it. But the program still thought 2 had been selected and wouldn't let me put the 2 in the correct box. I had to clear the entire puzzle and start over again. This bug needs to be addressed.