Meaning of strength training presets

When creating a training i have the following choices : 

I would like to know the difference between the two Recover steps as the input mask is the same. Is it a bug ?

Also, whats the use case between Recover and Rest ?

When recovering with a cooling period between workout series, should one use Recover or Rest ?

also, there is a bug when using Recover step (the default use at startup when creating new workout) if you want to change from Lap to Duration whitout setting an exercice : Save is disabled ...