Join makes splines instead of polylines

[Anonymous]

Just upgraded to AutoCAD 2016. In past versions when I joined lines it used to make them polylines. Now it is making them Splines! It also creates Splines if i pedit and join the lines and arcs. There appears to be a change in who the software works with arcs, as It seems to always convert an arc into a spline. I use AutoCAD because i could trust, splines are worthless to me.

1. Is there a new system variable I need to change? 

2. Why! Don't make me go back to the old AutoCAD version and need find / buy different software because of this huge lack of good judgement in changing a command that was not broken.

[rkmcswain]

There is one duplicate entity. That is causing funky joining (more than one entity) in general, but what is causing the Spline to be created is some of the lines have a non-standard extrusion direction. See the image below.

I removed that using the FLATTEN command, then JOIN works as expected.

[Matthew.SchwartzNZ4U4]

YES, set your PLINECONVERTMODE=1
It is a drawing setting and it is so annoying when it is toggled, so I add it to SYSVAR.