is there a thread in the BI forum about it?
how do you call/execute the code? what is the call/execution tree? where is the code defined and where is the file to be found?

yep
there is a seperated BI forum thread about it:
http://forums.bistudio.com/showthread.php?180959-unexpected-script-runtime-issue-when-putting-much-code-into-variables-by-a-seperated

now to how everything gets callen, where what is defined, etc.
but due the size of the projects i will stick to those section inbound in this problem (i will use github links so everyone can check the code without asking for it)

the functions are defined in 3 config.cpps:
https://github.com/X39/XLib/blob/master/X39_XLib_KeyCatcher/config.cpp
https://github.com/X39/XLib/blob/master/X39_XLib_ActionDialog/config.cpp
https://github.com/X39/XMS2/blob/dev_X39/X39_MS2_Scripting/config.cpp

registering of the button actions:

1. (auto) https://github.com/X39/XLib/blob/master/X39_XLib_KeyCatcher/Functions/init.sqf
2. (auto) https://github.com/X39/XLib/blob/master/X39_XLib_ActionDialog/Functions/init.sqf

2.1 https://github.com/X39/XLib/blob/master/X39_XLib_KeyCatcher/Functions/registerKey.sqf

3. (auto) https://github.com/X39/XMS2/blob/dev_X39/X39_MS2_Scripting/Functions/initMod.sqf

3.1 https://github.com/X39/XMS2/blob/dev_X39/X39_MS2_Scripting/Functions/initModHelpers/addInteractionMenuEntries.sqf
3.1.1 https://github.com/X39/XLib/blob/master/X39_XLib_ActionDialog/Functions/registerAction.sqf

executing a button action

1. initial key event registered by X39_XLib_KeyCatcher
2. https://github.com/X39/XLib/blob/master/X39_XLib_KeyCatcher/Functions/cb_KeyDown.sqf

2.1 https://github.com/X39/XLib/blob/master/X39_XLib_ActionDialog/Functions/createDialog.sqf
2.2 https://github.com/X39/XLib/blob/master/X39_XLib_ActionDialog/Functions/initSystemVariables.sqf
2.3 https://github.com/X39/XLib/blob/master/X39_XLib_ActionDialog/Functions/initActions.sqf
2.3.1 depending on what button was pressed (and if the condition of the actions return true) different code registered in https://github.com/X39/XMS2/blob/dev_X39/X39_MS2_Scripting/Functions/initModHelpers/addInteractionMenuEntries.sqf will be executed

for the working part it is more or less the same but that you register the actions then directly inside the debug menu so you only got the https://github.com/X39/XLib/blob/master/X39_XLib_ActionDialog/Functions/registerAction.sqf call (no seperated one)

Your code logic is somewhat complex and as such I may misunderstand your intent.

{
if(_x getVariable ['X39_MS2_var_UnitInitialized', false]) then
{

		_unit = _x;

};
false
} count attachedObjects X39_XLib_var_ActionDialog_Executor;

This design seems not safe/defensive programming.

---

My suggestion:

private ['_attachedObjects','_unitFound'];
_attachedObjects = attachedObjects X39_XLib_var_ActionDialog_Executor;//not necessary
_unitFound = false;
{
private ['_currentUnit'];
_currentUnit = _x;
if (!isNil '_currentUnit') then
{

		if (!isNull _currentUnit) then
		{
			if(_x getVariable ['X39_MS2_var_UnitInitialized', false]) then
			{
				_unitFound = true;
			};
		};

};
if (_unitFound) exitWith {_unit = _x;};
} forEach _attachedObjects;

If you can be sure _attachedObjects doesn't contain undefined units or removed units, the isNil and isNull check is obsolete.

Also you should not need to private _x as its a special variable as the engine sets the scope itself (at least thats the current knowledge and how Squint handles it).

Overall I don't get why you use the {} count array construct here.
If you want to catch the last unit in _attachedObjects that contains your variable, just ditch the exit condition of my design.
Ref: https://community.bistudio.com/wiki/count

changed the design many times trying while to fix that problem
the first attempt did not contained any variable as you can solve everything without a single one (attachedObjects will return an empty array if no object is attached)

im using count because it is faster (at least it was ... not sure about now but im used to this by today ^^ works the same way but without the _forEachIndex variable) but ... yeah
already tried it with foreach too

-----edit-----
Also the code is working (just how/when/whatEvar it is registered using the registerAction function makes the difference)

can be closed due the comment i received on reddit ...
http://www.reddit.com/r/arma/comments/2bn5gu/sqf_i_surrender/
buttonSetAction does not supports SQF? the fuck BI?

raising new bug soon for this