i'm facing a problem with my fieldsets.
i have fieldsets that are collapsed in the config params. i want to put grids interior these fieldsets. and to show my fieldset collapsed in my render. the problem is that my fieldsets are empty.
And when i change the config param to
i get this error when i try to collapse them after data loading
this.el is undefined 
 if(this.collapsed || this.el.h...collapse', this, animate) === false){
is there a solution to show my fieldsets collapsed with grids or to avoid this error?

Thenk you in advance for your help