When adding pictures to a post the WYSIWYG editor does show the actual picture inline.
However if I edit that same post later it just shows the ATTACH BB codes.
Is there a way to fix this so that images are shown when editing a post?
Surely there must be an add-on of some sort cause the guys at MediaPortal have had this working flawlessly for years and I doubt they are on XF2 somehow.
Would it work with TinyMCE or some other editor?
I'm not aware of any add-ons that do it, but possibly. Note there is a difference in behaviour between posts that use IMG tags rather than posts which have attachments. The attachment stuff requires additional data to be fetched, and that's something we don't do in XF1. The issue is independent of the editor.
I just tested that on my installation and IMG does indeed work there but ATTACH does not.
Then I checked MediaPortal to see what BB code those images displaying in the editor were and they are indeed ATTACH.
I'll try get in touch with the admin there.