Widget sidebar only appears if my blog post has a 'featured image'.

I’ve been pulling hair over this for quite a while and I’m running out pretty fast.

Hope I can get some support here for this.

Here’s the blog page on my wordpress site, as you can see, there are some post without and some with the ‘feature image’ shown
http://www.jackalventure.com/blog/blog/

All is sweet for posts with a featured image like this one (left sidebar is there, as expected)
http://www.jackalventure.com/blog/django-and-virtual-environments-a-better-understanding-i-hope/

Those without a featured image like this one
http://www.jackalventure.com/blog/back-on-the-bike-and-barefoot-outings/
the left sidebar has somehow disappeared

I want the sidebar to appear, regardless of whether there is a featured image or not. Can’t seem to figure this out.

Thanks and hope to hear some ideas soon!