Descriptive Problem Summary:
As BLEND_MULTIPLY requires hardware acceleration to be available, it used to fall back to the default blending mode. Note the past tense in my sentence here. Objects with blend multiply flat out turn invisible with HW acceleration disabled now.

Steps to Reproduce Problem:
https://dl.dropboxusercontent.com/u/107028026/ShareX/2017/ 01/blending.7z

Run this, toggle hardware acceleration in the client's options and watch how the blue squares turn invisible instead of becoming opaque.

Expected Results:
The squares would fall back to a different blending mode instead of disappearing altogether.

Actual Results:
They disappear.

Does the problem occur:
Every time? Or how often? Every time
In other games? N/A
In other user accounts? Yes
On other computers? Yes

Did the problem NOT occur?
Worked in 509.1319, 510.1320 broke it.

Workarounds:
No clue!