Picture converted to very low quality while sharing on Google + I'm using a HTC ONE X with Android 4.2.2 and HTC Sense 5.0

I took a screenshot from my phone : the picture has the same resolution as my screen which is 720x1280.

Then I share it on google plus :


go to 'Galery' app ( don't know if its the standard android one or an HTC specific app :/ )
choose my picture
touch 'share'
chose in the list 'Google+' which open the google+ app to choose the circles I want to share with.
confirm.


The picture shared is then 180x320 !
All text is unreadable so the sharing doesn't make sens anymore :/

Does anyone know why ? And how to prevent this ? I'm connected using wifi connection so there's no need to scale down the picture I can upload the full size...
It seems like it fixed by itself... 

Now  can see the full size picture in my post on Google + without doing anything more.

My guess is : it uploaded a sample sized version of the picture in order to share my post instantaneously while the full picture was still uploading ...

Anymore informations on this from anyone would be nice.

Thanks :)