Use the attached project... then try to add a new dialog. A wrong constant is selected by default (should be MAIN_ADD that is a control). If you try to rename it (for example IDD_DEMO) you will see the error.
The IDE are currently using the following ranges:
1001 - 2000: dialogs
2001 - 3000: menus
3001 - 3500: accelerator tables
3501 - 4000: accelerator table entries
4001 - 6000: dialog controls
6001 - 8000: menu items
8001 - 10000: bitmaps, icons, cursors, ...
10000 - 12000: string table entries
12001 - xxxxx: menubars (Pocket PC)
The IDE will use the next free ID, from any given range, when assigning a new ID (just looking at the resources, not the symbols). If you already have a symbol with this ID - you see the effect you describe. Not really a bug, but maybe somewhat confusing....
Also found another bug (imho). If you add a new icon, the resource editor modify an existing icon.
I don't understand. Apart from the same problem as above, I can't find anything wrong with icons...
Pelle