That doesn't sound like a bug to me. When the screen says "1 RP," you get one RP. When it says "9 RP," you get nine RP. The fact that the underlying calculation special-cases RP under zero is an obscure rule, not a bug.
It is, however, something useful to know. And I guess that's why you posted it here and not on the bug thread.
-Max
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Bauchelain - "Qwik Ben iz uzin wallhax! HAX!"
Quick Ben - "lol pwned"
["Memories of Ice", by Steven Erikson. Retranslated into l33t.]