Weird variable thing in 8.1.5

[jonathandlynch at gmail.com]

I just created a button with this script:

On mouseup
  Put "test" into tTest
End mouseUp

It would not compile, producing the following error:

Compilation error at line 2 (Chunk: can't create a variable with that name (explicitVariables?)) near "tTest", char 15

Why would this happen?

Nobody would ever be able to use 8.1.5 if that always happened, so what would make it happen now?

Sent from my iPhone