Thanks for the answer. It is strange, that it is totally possible to change the long name to another window's short name, but not the other way around.
The result should be the same for the two examples:
//create workbook with short and long name "Name1"
newbook name:=Name1 option:=lsname;
//create workbook with short name "Name2" and long name "Name1"
newbook name:=Name2 option:=lsname;
page.longname$="Name1";
will work fine. However,
//create workbook with short name "Name2" and long name "Name1"
newbook name:=Name2 option:=lsname;
page.longname$="Name1";
//create workbook with short and long name "Name1"
newbook name:=Name1 option:=lsname;
will not. You would expect the same result for both. Either
(1) One workbook with both long and short name being "Name1" and one with short name "Name2" and long name "Name1".
or
(2) Some kind of error or unexpected Names like "Name3".