Changed comments in response to github remarks.

lib/coll.gi

@@ -3053,16 +3053,21 @@ end);
 InstallMethod( CanComputeIsSubset,"default: no, unless identical",
   [IsObject,IsObject],IsIdenticalObj);
 
-# avoid immediate methods triggering multiple type changes once the Size of
-# an object is known.
+# This setter method is installed to implement filter settings in response
+# to an objects size as part of setting the size. This used to be handled
+# instead by immediate methods, but in a situation as here it would trigger
+# multiple immediate methods, several of which could apply and each changing
+# the type of the object. Doing so can be costly and thus should be
+# avoided.
 InstallOtherMethod(SetSize,true,[IsObject and IsAttributeStoringRep,IsObject],
   100, # override system setter
 function(obj,sz)
 local filt;
   if HasSize(obj) and Size(obj)<>sz then
     if AssertionLevel()>2 then
-      # Make this an ordinary error to enter break loop so that one can
-      # investigate call order for debugging
+      # Make this an ordinary error (not ErrorNoReturn as suggested) to
+      # preserve all debugging options -- even use `return` to investigate
+      # what would have happened before this methods was introduced.
       Error("size of ",obj," already set to ",Size(obj),
         ", cannot be changed to ",sz);
     fi;

lib/csetgrp.gi

@@ -586,7 +586,12 @@ local d,fam,typ;
     ActingDomain,U,FunctionAction,OnLeftInverse,Representative,g,
     CanonicalRepresentativeDeterminatorOfExternalSet,
     RightCosetCanonicalRepresentativeDeterminator);
-  SetSize(d,Size(U)); # as own setter
+  # We cannot set the size in the previous ObjectifyWithAttributes as there is
+  # a custom setter method (the one added in this commit). In such a case
+  # ObjectifyWith Attributes just does `Objectify` and calls all setters
+  # separately which is what we want to avoid here.
+  SetSize(d,Size(U)); 
+
   return d;
 end);