Two strophies are the same strophies in terms of their id but the selection & colour change is not synchronized
When both strophe block does not have colour, change colour on one applies to the other (desirable)
When changing the colour of one strophe block after that, the colour of the other strophe block does not change. it only changes when user switch to single display then switch back to parallel display
The selection highlight only apply to the clicked strophe in both cases
In the background, both strophe will be added to the array of selected strophies despite they have the same id if user click on both of them one by one