
3-1-6 & 3-1-7

3-3-7 & 3-3-8

4-1-9 & 4-1-10

4-2-8 & 4-2-9

4-5-6 & 4-5-7
4-5-8 & 4-5-9

4-6-6 & 4-6-7

6-2-9 & 6-2-10

6-3-6 & 6-3-7

6-4-2 & 6-4-3

6-6-4 & 6-6-5
6-6-7 & 6-6-8

7-1-8 & 7-1-9

9-3-1 & 9-3-2
They are absolutely the same blocks. For example: If I place 9-3-2 and select it with Ctrl+Leftclick they 9-3-1 will be selected.
This is just a list of the Blocks that get duplicated when I open the Stadium Competition Titlepack. It seems like the duplicated blocks depend on the Titlepack you use.
HOW TO REPRODUCE:
Step 1: Open TM² Stadium.
Step 2.1: Go to a Server of another Titlepack via TM² Stadium Serverlist.
OR
Step 2.2.1: Close TM² Stadium.
Step 2.2.2 Open another Stadium Titlepack.
Step 2.2.3 Go to a Server of that Titlepack OR open a map in local play OR open a map in Editor.
Step 3: Close that Titlepack.
Step 4: Open TM² Stadium.
Step 5: Open the Editor.
The more Titlepacks you open the more blocks will be duplicated. They can even appear 3, 4, 5, ... times.
Works for me 100%.