Interesting. So, it looks like it depends on whether Perl thinks the v-strings are valid barewords? A simple test:

#!/usr/bin/perl -w
for (0..255) {
   print "$_: ";
   eval "print -$_.0.0.1;";
   print "\n";
}
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That reveals that [\w\-\+] all lead to no warnings. [A-Za-z_] (i.e. 65-90,95,97-122) are valid bareword starters. [0-9] (i.e. 48-57) lead to actual numbers. I don't understand "-" and "+" (i.e. 43 and 45).

So it looks like Perl is aggressively changing v-strings into strings at compile time, and re-injecting those strings into the tokenizer. Weird....