wpmu migrated to a new server, mysql problems

2 weeks ago I migrated to a new server and everythign seemed to go smoothly. Now I noticed that when I click i.e. onto a comments table, i.e. wp_1_comments I get the following warning using phpmyadmin:

More than one INDEX key was created for column "comment_approved"

these are the existing indexes:

Documentation Keyname Type Cardinality Action Field
PRIMARY PRIMARY 0 Edit Drop comment_ID
comment_approved INDEX None Edit Drop comment_approved
comment_post_ID INDEX None Edit Drop comment_post_ID
comment_approved_date_gmt INDEX None Edit Drop comment_approved
comment_date_gmt INDEX None Edit Drop comment_date_gmt

the problem is that all blogs I create from now on, have this problem :slight_frown: any hints?