There's s an asynchronous problem when hitting the plus or minus button on large sets of repeatable metadata. Example: http://zs.thulb.uni-jena.de/receive/jportal_jparticle_00196062
As you can see there's alot of 'Sonst. Titel' in the mycore object. If you hit the repeater button's before mycore can handle them it leads to an exception which causes the loss of the new entered data.