No .. its a bug in your understanding of local variables and
with the stupid way var (doesn't) create local variables
unless its inside a
function (in your case it isn't)
The problem here is that in the nameless function being
called by the
interval, there is no way for it to find the variable 't'
which lives inside
the timeline of the scene/clip where you put this script.
thinks you must be using some local variable called 't',
which is undefined.