Multi-value script functions (or at least some like $inmulti, $setmulti) currently work by converting to a string and then working on the string. This has two problems:
a. They handle any string with a semi-colon in it incorrectly;
b. $Inmulti searches for the substring in the multi-value converted to a string, which is not the same as searching for one of the values matching exactly. (For the latter you should use $in rather than $inmulti.)
As a real example:
$inmulti(%artists%,Bob Marley) will be true if %artists% = ['Bob Marley','The Wailers'] or ['Bob Marley and The Wailers'] which is not going to work as expected.