Dynamic Field Bug? Mass update of any field populates dynamic fields

Not sure if this is a bug or maybe something not setup right. Looking for feedback.

So I create a field:

Opportunity Type: lets say 1, 2, 3

Then a Dynamic Field for Stage, let’s say 1A, 1B 2A,2B, 3A, 3B (And a blank)

It works fine I can select the stage, or I can leave it blank based on the Opportunity type.

HOWEVER, let’s say I do a mass update to change anything lets say “currency”. All of the blank Stages that are modified by the mass update are populated with 1A (Event though I have a blank first in the list)

Is this a bug or do I have something configured wrong. This field should not get populated by mass update if I have not even selected to change it.

Anyone else (BTW, I’ve tested on two installations and two different version of 7.12 and 7.10