Strange behaviour when using CAPS for a slot name

Steve, I see rather strange behaviour when using caps for a variable name. See below:

Io> 55 type
==> Number
Io> aa:=55
==> 55
Io> 55 type
==> Number
Io> AA:=55
==> 55
Io> 55 type
==> AA

So by using a caps slot name during a slot assignment, the type of the subject of that assignment is changed to the name of the slot. Not sure why this is happening but I'm guessing it was not intended.