1. Place a unit in the editor and name it test_unit

2. Init.sqf:

_anims = [
"ainvpknlmstpsnonwrfldnon_ainvpknlmstpsnonwrfldnon_medic",
"AinvPknlMstpSnonWrflDnon_medic0s",
"AinvPknlMstpSnonWrflDnon_medic",
"AinvPknlMstpSnonWrflDnon_medic0",
"AinvPknlMstpSnonWrflDnon_medic1",
"AinvPknlMstpSnonWrflDnon_medic2",
"AinvPknlMstpSnonWrflDnon_medic3",
"AinvPknlMstpSnonWrflDnon_medic4",
"AinvPknlMstpSnonWrflDnon_medic5",
"AinvPknlMstpSnonWrflDnon_medicend"
];

sleep 1;

test_unit playActionNow "medicStart";

sleep 1;

_anim = (animationState test_unit);
hint format["%1 (%2)", (_anim in _anims), _anim];
diag_log text format["%1 (%2)", (_anim in _anims), _anim];

while {(_anim in _anims)} do {

_anim = (animationState test_unit);

hint format["%1 (%2)", (_anim in _anims), _anim];
diag_log text format["%1 (%2)", (_anim in _anims), _anim];

sleep 1;

};

3. Result will be:

true (ainvpknlmstpsnonwrfldnon_ainvpknlmstpsnonwrfldnon_medic)
true (ainvpknlmstpsnonwrfldnon_ainvpknlmstpsnonwrfldnon_medic)
false (ainvpknlmstpsnonwrfldnon_medic0s) <-- FALSE - EVEN THOUGH THIS IS INSIDE THE _anims ARRAY

Same is true for direct comparison like:

if ((animationState test_unit) != "ainvpknlmstpsnonwrfldnon_ainvpknlmstpsnonwrfldnon_medic"
&&
(animationState test_unit) != "AinvPknlMstpSnonWrflDnon_medic0s"
&&
(animationState test_unit) != "AinvPknlMstpSnonWrflDnon_medic"
&&
(animationState test_unit) != "AinvPknlMstpSnonWrflDnon_medic0"
&&
(animationState test_unit) != "AinvPknlMstpSnonWrflDnon_medic1"
&&
(animationState test_unit) != "AinvPknlMstpSnonWrflDnon_medic2"
&&
(animationState test_unit) != "AinvPknlMstpSnonWrflDnon_medic3"
&&
(animationState test_unit) != "AinvPknlMstpSnonWrflDnon_medic4"
&&
(animationState test_unit) != "AinvPknlMstpSnonWrflDnon_medic4"
&&
(animationState test_unit) != "AinvPknlMstpSnonWrflDnon_medicend") then {};

Condition will be FALSE although is should/must be TRUE.

WTF.