I have two seperate sites (subdomains) which are on two differrent installation of drupal. They share the user and session table so the user can seamlessly move around the sites with single signon. The new registration is possible only on one site. Both sites are on drupal 5.14. The sites are not "multisite" is strict drupals sense since these are different instances(code base + database) of drupal. In fact I configured this way as I was aware of the likely senario below.
Now on site A, for all modules 6.x stable release available. For site B, for some modules, 6.x version is still not available. I am wondering what will happen if I upgrade on Site A to 6.x but still share the user and sessions table with site B which will remain at 5.x? It seems harmless aparently but just want to understand if there are any gotchas I am not aware of.
Any thoughts?