If your actual code looks more like this:
if (something)
{
myName = "Henry";
myCustomFunction( argname=[ myName, "Thierry" ] );
}
Then it's because the literal struct and array notation in CF is very badly written and buggy.
If you can confirm the circumstances it breaks, raise an issue with Adobe (there are several issues relating to this already; you may or not feel like checking for duplicates).