Theme CSS is not fully applied via set_theme if setting theme without a redescribe

[ainslec]

Theme CSS is not fully applied via set_theme if setting theme without a redescribe.

It seems that directions retain the theme settings of the previous theme (in the example below, directions in the text are styled as per the prior theme).

start_at    = loc_1
start_theme = theme_1

locations {
   loc_1 : location "You are going to the east.";
}

## If use on_pre_describe here, then it works !
on_pre_tick {
   : set_theme "theme_2";
}

themes {
   theme_1 : theme / colors {
      paper = "0"
      pen = "15"
   }
   theme_2 : theme / colors {
      paper = "15"
      pen = "1"
   }
}