Player V10.13.17
To reproduce:
1. Open a level that has more than one skill.
2. Select any skill in the skill selection panel that is not the first skill.
3. Press the backwards frameskip hotkey. The first skill will automatically be selected when this happens.
See GIF below as an example. After starting the level, I clicked on the miner skill. However, when I backwards frameskipped, it automatically selected the very first skill (the floater). This should not happen at all.