What steps will reproduce the problem?
1. Rename a set to "Default"

What is the expected output? What do you see instead?

Expected: An error.

Seen: The rename is accepted, but leads to undefined behaviors and kills future renames.

What version of the product are you using?

3.2.0.2.0

Do you have an error log of what happened?

No, but future attempts to rename sets fail with this:

Date: 2009-08-27 12:24:39
ID: 1
Error occured in: Global
Count: 1
Message: ..\AddOns\ACP\ACP.lua line 443:
   attempt to index a nil value
Debug:
   (tail call): ?
   [C]: ?
   ACP\ACP.lua:443 OnAccept()
   ..\FrameXML\StaticPopup.lua:3282 StaticPopup_OnClick()
   [string "*:OnClick"]:1:
      [string "*:OnClick"]:1
AddOns:
  Swatter, v5.6.4424 (KangaII)
  WowheadLooter, v30201
  AckisRecipeList, v1.0 3.2 Beta 2 2323
  ACP, v3.2.0.20
  AdvancedTradeSkillWindow, v
  ArkInventory, v3.02
  AtlasLoot, vv5.07.05
  AtlasLootFu, vv5.07.05
  AucAdvanced, v5.6.4424 (KangaII)
  AucDb, v5.1.DEV.3583
  AucFilterBasic, v5.6.4424 (KangaII)
  AucFilterOutlier, v5.6.4424.2531
  AucMatchUndercut, v5.6.4424.2531
  AucStatHistogram, v5.6.4424 (KangaII)
  AucStatiLevel, v5.6.4424 (KangaII)
  AucStatPurchased, v5.6.4424 (KangaII)
  AucStatSales, v5.6.4424.2842
  AucStatSimple, v5.6.4424 (KangaII)
  AucStatStdDev, v5.6.4424 (KangaII)
  AucStatWOWEcon, v5.6.4424.2530
  AucUtilAHWindowControl, v5.6.4424.3311
  AucUtilAppraiser, v5.6.4424.2530
  AucUtilAskPrice, v5.6.4424.3175
  AucUtilAutoMagic, v5.6.4424.3142
  AucUtilCompactUI, v5.6.4424.2530
  AucUtilEasyBuyout, v5.6.4424.3583
  AucUtilFixAH, v5.6.4424 (KangaII)
  AucUtilItemSuggest, v5.6.4424.3108
  AucUtilPriceLevel, v5.6.4424.2545
  AucUtilScanButton, v5.6.4424.2530
  AucUtilScanFinish, v5.6.4424.2530
  AucUtilScanProgress, v5.6.4424.2530
  AucUtilSearchUI, v5.6.4424.3655
  AucUtilSimpleAuction, v5.6.4424.0
  AucUtilVendMarkup, v5.6.4424.2530
  AutoDing, v2.4.1
  Babylonian, v5.1.DEV.130
  BeanCounter, v5.6.4424 (KangaII)
  BrokerBags, vv1.4-Release
  BrokerClock, v1.0
  BrokerMoney, v1.36
  BulkMail2, v3.0.0
  Cartographer, v2.0
  Cartographer3, v3.0 v0.11.2
  CartographerBattlegrounds, v2.0
  CartographerCoordinates, v2.0
  CartographerFoglight, v2.0
  CartographerGroupColors, v2.0
  CartographerGuildPositions, v2.0
  CartographerInstanceLoot, v2.0
  CartographerInstanceMaps, v2.0
  CartographerInstanceNotes, v2.0
  CartographerLookNFeel, v2.0
  CartographerNotes, v2.0
  CartographerWaypoints, v2.0
  CartographerZoneInfo, v2.0
  ChatBar, v2.7
  Chatter, v1.0
  Configator, v5.1.DEV.130
  CurseProfiler, v
  DebugLib, v5.1.DEV.130
  Enchantrix, v5.6.4424 (KangaII)
  EnchantrixBarker, v5.6.4424 (KangaII)
  epgploot2, v2.0.11
  FishingBuddy, v0.9.8b
  FlightHUD, v0.8.7
  Flightmap, v
  Fortress, v1.12
  FriendsShare, v
  Gatherer, v3.1.14
  GathererHUD, v3.1.14
  GathererDBWowhead, v1.0.2009-02-18
  Grouper, v3.07
  GuildLaunchProfiler, v00.09.18 BETA
  HealBot, v3.2.0.4
  LightHeaded, v297
  LootLink, v3.51
  Macaroon, v30100.2.6
  MacaroonBound, v30100.2.5
  MacaroonCB, v30100.2.5
  MacaroonLoot, v30100.2.5
  MacaroonXP, v30100.2.5
  MacaroonXtras, v30100.2.5
  MapNotes, v5.16.30200
  MapNotesBrowser, vv1.00.30200
  MapNotesIconLib, v1.04.30200
  MapNotesIconLibFancy, v
  MapNotesIconLibLegacy, v
  MapNotesIconLibNeptunia, v
  MapNotesIconLibNumbers, v
  MikScrollingBattleText, v5.4.64
  MinimapButtonFrame, v3.0.7
  MinimapButtonFrameSkinPack, v3.0
  MissingFriends, v09.04.13
  Misspelled, v0.3.39
  Nauticus, v3.2.0
  NazScrooge, v1.77
  Neatfreak, v1.4
  NotesUNeed, v6.58.30200
  Outfitter, v4.7.4
  Overachiever, v0.46
  Pawn, v1.2.4
  Postal, v3.2.0
  QuestHelper, v1.1.13
  ReagentRestocker, v0.9c
  RecipeRadar, v1.32
  Recount, v
  RecountThreat, v
  SharedMedia, v3.0
  SmartMount, vv3.1-92
  Stubby, v5.6.4424 (KangaII)
  SwindlerPreventer, v3.1.3
  TipTac, v09.08.26
  TipTacItemRef, v09.08.13
  TipTacTalents, v09.04.17
  Torta, v0.2
  WinterTime, v1.81
  BlizRuntimeLib_enUS v3.2.0.30200 <us>
  (ck=cc5)

Please provide any additional information below.