I think you need to clear default app settings by going to either:
- Settings > Apps/Applications > Default Applications, and the clear all.
or
- Settings > Apps/Applications > Google+ > Clear Defaults
and redo the previous operation for Picasa and Gallery and then try sharing again.
It should give you the options to choose the app you want to use and give you the options to use same app every time or just once, select just once in order to use a different app every time.
Hope this works!