TIG-- this is my last report on the subject and I will outline my precise actions for you.
In your instructions above you indicate an instruction to type 1" + <return>.
What I've discovered is that if I activate the fillet tool-- per your exact rectangle instructions above--- and I use the cursor to highlight the default 0" value shown in the radius dialogue THEN delete or type 1" + <return> the value goes back to 0" and the tool does not work and this would be the method I was trying previously.
If I activate the fillet tool and type the value 1" + <return> directly (without highlighting with the cursor) the 1" value holds and I can click and select Line 1, but selecting Line 2 takes several tries before it works (like 3 or 4). I also get an input line-based cursor this method, not my default arrow. This is a method I had tried previously. I then did the operation again, only this time I typed 1" + <return>, then 1" + <return> a second time, then select Line 1, then I could select Line 2 immediately and the tool worked. I verified this on 3 straight operations.
If I activate the fillet tool and type 1 + <return> (did not type " after the 1 per your instruction) the value holds as 1", I can select line 1 & 2 and the tool works perfectly every time. I have not had it fail on 5 straight operations. Cursor arrow remains as well.
Ruby console was open the entire time on all attempts with no error showing up in the window at any point.
Sorry if I missed something along the way, but this is how the tool is operating for me. I hope some frustration for others may be avoided in the future. Thanks for all the work you've done. I use a couple of your plugins they are very useful. I now know how to use this tool on my system whether or not this is the way it should work. I'm just glad I now know.
Cheers-