I just experienced the same bug.
I attached the problematic level.
1) Put the attached level to levels forder and play it with Neolemmix 12.12RC.
: You can see that the level gives you 1shmmier, 1climber, 1swimmer, 1bomber, 1stone,r 1platformer and 1builder.
2) Now close the Neolemmix 12.12RC and open the same level with editor V1.37.
: All the skills are reset to zero. It's fine if don't save the level though.
3) Open any other level with editor V1.37 and then open the attached level.
: Now all the skills are changed to the skillset of the level you opened previously.