IDE Display changed to 'fixed pitch' ???

[J-G]

Now I'm confused 

I've been using Lazarus since last August and believe that I've always used ZapfCalligra as the font in the Source Editor   -  until two days ago   when the display changed dramatically. It was only upon noticing that the font had suddenly become 'Courier'     that I tried to re-select Zapf and discovered the wide-spaced issue.

I'm also having difficulty understanding the arguments about proportional fonts (by far the majority) and difficulty in dealing with tabs, indentation etc. .... ????   
All Editors/WordProcessors handle this perfectly well.