Setup: 
* KendoUI Community Edition v2013.2.716
* Multiple resources in event

When Field in Event contains Array of guids - it shows fine in the event, but on grouping throws an error (as guids are treated incorrectly in filtering function)
When guid is wrapped by '', then grouping works well, but Event do not show assigned resources...
Using debugging I found that problem is in filtering (Piece from the code): for(r=a.filterExpr(e),s=r.fields,d=r.operators,o=c=Function("d, __f, __o","return "+r.expression),(s.length||d.length)&&(c=function(e){return o(e,s,d)})