The syntax for the suffix notation is

EXPR while EXPR;
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and not

EXPR while ( EXPR );
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Therefore, you are comparing apples and oranges.
In while() { print "1\n" }, the expression is "".
In print "1\n" while ();, the expression is "()", the empty list, which is false in boolean context.

You're right about there being an inconsistency, though, just not the one you mentioned.

>perl -MO=Deparse -e"while() { print 1 }"
while (1) {
    print 1;
}
-e syntax OK

>perl -MO=Deparse -e"print 1 while;"
syntax error at -e line 1, at EOF
-e had compilation errors.
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