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Start: we have a single 
region with deactivated 
region fade in/out:        | i                              i |
 
Split 1:                                     v
ok, so far ...             | i             i | i            i |

now:
drag region fade in:                         .>>>.
the fade in of the second  | i             i | a            i |
region is automatically 
activated. that's ok.

now split the second 
region, again:                                        v
Error: the beginning of    | i             i | a     i|A    i |
the now 3rd region has an
activated fade in!

Now let's undo this step 
by step: undo 2nd split    | A             A | a            A |
ERROR: expected is:        | i             i | a     i|A    i |
 
      
all further undo steps now 
contain wrong fade in/out                    .<<<.
activation state, undo drag| A             A | A            A |
ERROR: expected is:        | i             i | i            i |

undo 1st split:            | A                              A |
ERROR: expected is:        | i                              i |