Recombinator choosing the item base doesn't seem random

In the description of the recombinator bench, it states that, in case of success, the base is chosen at random. I successfully recombinated the same exact 2 mods 15-20 times and in every case it chose the "wrong" base.

Item 1:
Seaglas spear with a T4 hybrid Phys+accuracy mod

Item 2:
Any spear base with a t9 flat accuracy mod

In every case of success, the base of item 2 was chosen. It is possible I just got unlucky, however, the chances for that are quite low. That would be ~1/32000 in case of 15 outcomes in a row and ~1/1000000 in case of 20.
(I dont have an exact number of successful outcomes sine I didn't start counting right away. I didn't expect it to take this long, and some successful outcomes I already sold or recombinated multiple times )

I don't get it, so is it choosing the attributes from the 2nd applied item mainly? Or is it selecting say the first 3 attributes of item 2 and the last 3 of item 1? How's it not random?

The issue I have is with the selected base and not the mods. I included them just to describe the process in as much detail as possible.

I am also 11 - 0 on successful recombs selecting the non seaglass base every time. It is either bugged or there is rule we don't understand. At first I thought maybe the ilvl of the seaglasses i was using was preventing the transfer of t1 mods so i switched to to ilvl 82 seaglass only and still failed 6 in a row. The extremely high price of fractured seaglass base bespite fractuing orbs and recomb attempts being very cheap supports the conclusion that it is broken.

I tried this myself and encountering the same issue. It seems that the base type chosen is weighted towards the item that has the rarer mod on it. That is the only explanation.