Abyss Currency Overwriting Suffix Despite Open Prefix - Bug or Intended?

Yesterday I bought a ring with full suffixes and an open prefix and used Collarbone on it. One of the revealed mods was obviously a suffix mod - "Recover #% of Maximum Mana on Kill" - which I overlocked and applied. it overwrote my existing mod "Leech #% of Physical Attack Damage as Mana", even though there was an open prefix. Is it a normal for the game to propose/reveal suffix mods when suffixes are already full and an open prefix is present? Is this intended, or is it a bug?

https://www.imagebam.com/view/ME190M36

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seaman#4993 wrote:

You don't have open prefix. Flat mana and % mana are two different mods.
If modifiers are full, desecrating removes a random modifier.
The choice of prefix or suffix occurs during desecrating, not revealing.

Oh man you are right. There is no tier on the %. I was losing it:)