How does the 'Load Custom Level' button work in Hexcells Infinite?

On the Main Menu screen of Hexcells Infinite, there's a button on the bottom right that says 'Load Custom Level'.

However, when I click it, the button does not seem to do anything. It doesn't open any sort of dialog or a file selection window, or anything at all.

Does this button do anything? If it does, how does it work?

Loading a custom level involves copying the desired level's data onto the clipboard and clicking on the button with that data on the clipboard.

For example, this butterfly-shaped level (taken from here):

Hexcells level v1
Symmetry
sekti
What a beautiful butterfly! Just look at that blue and black pattern it has!
Mesmerising! And it's fully symmetric, too!
..................................................................
..................................................................
..................................................................
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..........................o+..........O...........................
............................o.......o+............................
....................................../+..........................
............................o+......o.............................
..............................x...x+..............................
..................................................................
......................o.......x+..x.......o.......................
....................o...o.......o+......o...o.....................
......................x+..o...x...x...o...x.......................
....................o...x+..on..o+..o...X...oc....................
......................x...x...o...o...x...X.......................
....................o+..x...o...o+..o...X...o.....................
......................o...o+..x+..x...o...o.......................
........................o...o...o+..o...o.........................
......................o...x...x...x...x...o.......................
........................x...o...o+..o+..x.........................
......................o...o+..o...o+..o...o.......................
........................o...o...x...o+..o.........................
..........................o...x...x...o...........................
........................o...o...x...o+..o+........................
..........................X...o...o+..x...........................
........................o...X...x+..x...o.........................
..........................X...o...o...x...........................
........................o...x.......x...o.........................
..........................o+..o...o...o...........................
............................o.......o.............................
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..................................................................
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(Note: The lines at the beginning must also be copied as part of the level data. They contain information about the level such as the name, author and an optional level description displayed underneath the puzzle field.)

Will bring up the level like so:

It is also possible to load a list of levels by copying multiple levels onto the clipboard at the same time.

Levels can be found from this subreddit right here and are made in a level editor called SixCells (made by fellow StackExchange user Oleh Prypin, AKA BlaXpirit).