As discussed above the DS1.11 (an endurance pad I believe), first needs to be bedded in, in accordance to Ferrodo procedures and will "key" the disc as a result. Having run them on my R26.R I know that they provide a very even performance and drag coefficient (.46) providing they stay within their temperature range (200°-700°C). The pad pickup, as it sounds like you experienced (warping of a disc is actually rare on large discs) is usually from "shocking" the pad by providing heat too quickly to a non bedded pad and disc combination. It can also happen by "dragging" the brake when the pads are cold creating unnecessary heat entering a braking zone rather than the more race like approach of threshold braking.
Not being worked hard enough in normal conditions is unlikely to leave deposits. It's being worked too hard too quickly that does this.
The new textar pad (and most likely a different compound will of course cut the old compound off the disc as it tries to key itself. This would have created the perceived remedy.
Pads should be bedded in in all situations and ideally to a new disc surface free of previous compounds. DS1.11 is a race pad and the expectation of the manufacturer is that this is happening with their products as it is usual in their typical environment. Therefore judgment is being made on the product in an environment where it is not intended to be used (track days for example, where few will actually get a pad and disc combination up to the ideal working temperatures consistently).
As for asking a race pad not to squeal? Well, thats out of the scope of design for a pad intended to be used where noise and vehicle harmonics are the least of the designers worries.
All good practice nonetheless and its easy for me to pass comment having learned these lessons years ago (I am old) Hopefully this will help you in the future.
Learn the characteristics of pad and how your driving might affect it.
Then understand the specific process for bedding that type of pad in (they tend to vary a little from manufacturer to manufacturer and compound to compound.
Some instruction on threshold braking and circuit driving characteristics also helps
And (as one famous driver was once told when he complained about his brake fade at Lemans) brake less!!!!