Translucency-plates getting clipped

Dear skilled people,

I’m stuck in a DOF situation. I have some planes with translucency materials on them.
And to keep the details in the opacity mapping of the texture, I have settled for a “non-DOF plane” situation, meaning, I want to have everything rendered with DOF, but not the planes.
AND I know that the translucency materials, when set to “after DOF”, I get what I’m looking for. Though, for some odd reason, when moving the focus point in front of the planes, they suddenly go from not DOF’ed to FULLY DOF’ed.

My understanding is, that when the planes enter the “out of focus background area” of the DOF, they get the full effect, but I don’t understand that they get totally out of focus abrubtly, especially, when they have the “after DOF” setting. Then they shouldn’t be concidered for any kind of blurring effect.

When I inspect the “seperate Tranclucency Alpha”, I can see, that the planes entering the “out of focus background area”, disappears in this buffer.

Here’s a link to a vimeo clip, that shows the issue: Translucency issue

So finally, my question is:

Does anybody know, how to “force” the planes to NOT disappear in this buffer, when the focus point of the camera gets a fair bit in front of the planes?