Line wrap problem - Pluma 1.16.1 on Debian 9.1

[Richard Owlett]

I wanted to have line wrap occur at column 70.
I went to Preferences->View.
Line wrapping was indicated as enabled.
I selected "display margin" and set the margin to 70.
Margin displays.
Text does *NOT* wrap.
I also tried a reboot from power-off - no luck.