change pandas behavior

mrdna/readers/segmentmodel_from_cadnano.py

@@ -226,7 +226,7 @@ def gen_prop_table(part):
     for i,v,z,f in zip(not_stacked, vh,nzid,fwd):
         key = (v,z,f)
         if key in _hashtable:
-            nt_prop['stack'][i] = _hashtable[key]
+            nt_prop.loc[i,'stack'] = _hashtable[key]
 
     devlogger.debug(f'  Building 3prime')
     tprime=[]