Confused about expressions in Prime RPN stack

[Orome]

This may be a pretty basic question, but it has me stumped.

I'm confused about Prime's handing of expressions on the RPN stack. When I enter an expression by, for example, keying in

['☐'][3][x2]

and then subsequently select it on the stack and hit [ENTER], I get not the expression I entered, but 3^2, stripped (apparently) of the surrounding '..', so that if I try to do anything with it I get a syntax error. This confuses me because it's possible to put things on the RPN stack that the Prime then treats as syntax errors when picked off the stack. What am I missing?

(I'd have expected something like the 48, where putting an expression in '..' in the stack, selecting it and hitting [ENTER], or otherwise picking it, gives back the '..' expression. To do that on the Prime, I need to first key in ['☐'] to "put back" the '..' and then [ENTER].)