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it seems that there is still a strong bug in T3 and t3_bs3_blank template.
This is the problem:
if you work on a joomla menu item and then you save your work, the ENTIRE megamenu configuration RETURNS TO THE DEFAULT: all the previous configuration work is lost!!!
Because of this I am forced to make an upload of the table "template_styles" in PHPMyAdmin each time I make the changes on the menu items, but it is a very frustrating problem.
This problem seems to have been solved on your post dated March 27 2015 - you wrote then: "megamenu got error when you use special character like "ü" and "ä" in "Item Caption" and its a bug, I have reported to dev team" - but it is still the same, and, in addiction, I don't use special character like "ü" or "ä" in "Item Caption".
Please investigate about this.