Recurring notifications about group creation

Hi,

I've created some groups and users got notification about these groups. However, the site still resends notification about "new" group every few days. The notification looks like here (please note the group creation date, the mail has been sent today);

Hi Peter Joe,

SIGs Admin created the Group “Learning and training pedagogies” on
Ed2.0Work SIGs on Sat, 03/09/2013 - 21:56:

How do we teach and train

Permalink: http://sigs.ed20work.eu/groups/learning-and-training-pedagogies

[...Rest of the email removed...]

Any ideas, help? It starts annoying registered users.

Best
VooVeek