The bug is related to using the "Groupings" feature with "Separate groups" settings for a Wiki.
If a student is in more than one group - for example 'A-group' and 'B-group' - and a 'Wiki-grouping' is created that includes 'B-group' in the 'Wiki-grouping', (but not 'A-group'), the Wiki opens in 'A-group' view for the student. The student then edits and saves information in the Wiki, but the Wiki is not listed in the available "Other Wikis" list, and cannot be viewed by the Teacher. This error only occurs if the student is in another group where the group-name of this other group is alphabetically lower than the group that has been included in the 'Wiki-grouping' (e.g. A-group is lower than B-group). Also when the Teacher initially accesses the Wiki, it opens for a group of the lowest alphabetically named group in the Course, even if that group is not included in the 'Wiki-grouping'.