Multilingual setting change causes repeat blog posts and other issues

I see various problems when I change the Multilingual System > content selection mode setting from option#1 to option#2. (i.e. change it from 'Current language and language neutral' to 'Mixed current language (if available) or default language (if not) and language neutral'.)

Is changing this setting on an active site expected to cause problems?

The most obvious issue is that the same blog entry is displayed repeatedly on blog pages, in some situations. The problems stop when I change back to the original multilingual setting.

I haven't been able to test this on a clean install, but I've tried to work out the main steps that created this issue in my case. (it may not be necessary to follow the steps exactly).

1 Drupal 6.6 site. Default language is English with no path prefix. In this example, User/1 is called User1

2 Add another language - In this example, we'll call this Language#2, and its path prefix is /LN/

3 Install i18n module and enable all sub-modules (site also has Views and CCK - maybe these are relevant)

4 Multilingual system -> Content Selection mode: Current language and language neutral.

5 Account > User1 > Language Settings -> English

6 Languages configure -> Path prefix with language fallback.

7 Multilingual system -> Content Selection mode: Mixed current language (if available) or default language (if not) and language neutral - This step triggers the issue

8 As User1, create a new blog entry. Set its language to Neutral

9 Go to [example.com]/blog/1 - the blog entry appears once - the expected behavior.
Switch to language 2 or go to [example.com]/LN/blog/1 - the same blog entry is displayed repeated many times.

Note: While the interface is set to language2, if I enable the 'Recent blog posts' block it also shows the same blog post title repeatedly, but only on admin pages and other system generated pages. And more widespread problems appear if user2's language is changed from English to Language#2.