When you use position: 'absolute' with bottom: the bottom offset is not respected like it is when the position is 'fixed'. Instead, it seems to "jump" right to the bottom when it hits it's bottom offset instead of halting the translateY increment steps.

steps to reproduce:

• setup a properly formed table, load required libs
• demonstrate correct behavior with $table.floatThead({position: 'fixed', bottom: -45});
• reset floatHead > $table.floatThead('destroy');
• swap out positioning strategy with: $table.floatThead({position: 'absolute', bottom: -45});
• ^ or just skip steps 2&3 and go right to 4 ;)

jsFiddle: https://jsfiddle.net/herringtown/ya59zo2h/2/

browser: Chrome 60.0.3112.113 (Official Build) (64-bit)
OS: OSX Sierra