Yes, it took me quite a while, a hex editor (for the output) and some documentation to see what's going on :-).

I tend towards seeing this as a bug. => is supposed to "force any word to the left of it to be interpreted as a string" (perlop). Also, it violates the principle of least surprise. I noticed that e.g. 0xC0 => "value" will be interpolated as well, though.