Where are my "thisUnit" names?

[Rob Lewis]

The simplest possible test: In the ON script of a unit, I put this: 

write log (thisUnit) & " ON script triggered" color red

What I get in the log is: 

 On script triggered [in red]

I even tried (thisUnit as text), which the compiler rewrote as ((thisUnit) as text). No dice. (According to XTension's sdef, thisUnit returns a text value, but still…)

What am I missing?