Join command is removing a node

[albionpjl]

This is driving me nuts because I can't work out what's causing it.
I had to construct a grid of narrow footing trenches for a plan.
I'm doing what I've done many times before without any trouble - I draw centre lines across the building footprint, offset .3m to either side of each line and delete the middle lines, then use the trim command to tidy up the places where the lines cross and then use join to join the individual lines together. (see attached file which is ready to begin joining.)
Now, while some lines are joining correctly (eg four lines joining to form a single polylnie in the shape of a square) with others, as soon as I hit enter after typing 'j' one of the nodes vanishes. ie what should be a square becomes a triangle. (see second attached file where I've joined several of the polylines and some have lost nodes.)

These are all 2d polylines created by me using the PL command, then trimmed and joined.  Does anyone know what could be causing this and how do I stop it?
It does make a difference which order I use when joining. Sometimes I can just select them all and it's fine, other times I have to pick one and join it to the next, then join that to the next, and then I can join up the last - but not every time. I can see no obvious variable affecting this.

C3d 2019

[Ranjit_Singh]

Convert the polylines to lightweight polylines using convertpoly. Then call the join command.

[tcorey]

I'm not sure why this is happening, but I can suggest two workarounds:

1. Explode all polylines down to lines and then use the JOIN command.

or

2. Use the PEDIT command, Multiple option, Join.

[albionpjl]

Thanks.
Explode worked and was nice and quick. Wish I knew why it's suddenly doing this, though. Never had any problem until the last couple of weeks.

[albionpjl]

I wonder if there's any connection with the fact that I just noticed that I have polylines and 2d polylines. I don't know how I ended up with two types because all were originally created using the PL command.

[albionpjl]

Further info on the bug.

If I create a poly line working in a clockwise direction, end the command, start the pl command again, and start the new line from where I left off, continuing to work in a clockwise direction until I get to where I started the first line, and then join those two lines using the join command, one node deletes itself.

If I draw the second line, starting from the the origin of the first line and work anti-clockwise until it reaches the end of line one, and then join them, it doesn't lose a node.

If the lines don't touch both ends, the nodes don't delete either.

Madness!

And yes, going into the pedit command and using join there does avoid the problem but also takes several clicks longer than just typing J.



And I'm sorry, but I don't accept a workaround as an actual solution to a bug.  Autodesk, hello?

[Ranjit_Singh]

As I posted earlier you are working with heavyweight polylines. Start using lighweight polylines. Heavy weight polylines store each vertex entity as a separate entity (even for 2d polylines) and when it detects two nodes on top of each other it considers it redundant and deletes that node during a join operation. It seems like your plinetype setting is 0. Set it to 2.

[albionpjl]

I did try your convertpoly suggestion earlier, which made no discernable difference.
However, I've changed the setting to 2 and will see how it goes. Thank you.