image description with line break

What are you typing in the image description field? You don't need to manually insert a "<br>" when you want to create a linebreak. Just a normal break will do, pluck will automatically convert it.

What version of pluck do you use?

Yes indeed, the album module seems to contain a bug. It has already been fixed for pluck 4.7, but you can fix it manually by following these steps:

1) open data/modules/albums/pages_admin/editalbum.php
2) find the line containing $cont2 = str_replace ("\n","<br>", $cont2);
3) cut and paste that line below the line containing $cont2 = htmlspecialchars($cont2);
4) done!