Bug: Selecting and completing the 2nd level in "Custom -> From Users" automatically completes the 1st one, too.
(Step 0: Start completely new.)
Step 1: Select level 2 in Custom -> From Users.
Step 2: Complete the level.
Step 3: Click on "Next Level".
Result: Level 2 restarts, level 2 is marked as completed, level 1 is marked as completed
Expected: Level 3 starts, Level 2 is marked as completed.
Reproduced with current Firefox and Chrome.