Corrects isfilter()

code/__DEFINES/is_helpers.dm

@@ -20,7 +20,7 @@ GLOBAL_VAR_INIT(magic_appearance_detecting_image, new /image) // appearances are
 
 // The filters list has the same ref type id as a filter, but isnt one and also isnt a list, so we have to check if the thing has Cut() instead
 GLOBAL_VAR_INIT(refid_filter, TYPEID(filter(type="angular_blur")))
-#define isfilter(thing) (hascall(thing, "Cut") && TYPEID(thing) == GLOB.refid_filter)
+#define isfilter(thing) (!islist(thing) && hascall(thing, "Cut") && TYPEID(thing) == GLOB.refid_filter)
 
 // simple check whether or not a player is a guest using their key
 #define IS_GUEST_KEY(key)	(findtextEx(key, "Guest-", 1, 7))