The phenomenon you're talking about is ice bridging, in which early application of deice boot pressure will inflate the boot, pushing soft ice outward, but not breaking it off. According to ice bridging proponents, the ice then remains in the shape of the inflated boot, and continues to build. The boot deflates, leaving a hollow channel beneath the ice. Each subsequent inflation of the boot fails to affect the ice, as it's built a "bridge" over the boot...the boot can no longer properly remove the ice.
In the USA, the Federal Aviation Administration and NASA have both come out in recent times and adamantly insisted that ice bridging is a myth, that it does not exist.
It does.
What the FAA is pushing is activation of the boots at the first sign of ice. Their stand, and also that of NASA, is that failure to activate the boots early in the icing process may prevent the boots from doing their job, too...too much ice and the boot won't work, either. They also don't want the ice to build up over the boots and then start building aft of them in the unprotected areas of the flying surface; when the boot does break away the ice over the boot, it leaves a ridge behind the boot which disrupts airflow. Take care of it early and keep inflating those boots, says the FAA.
I disagree, and most experienced aviators who have spent any significant time in icing conditions with boots will know that ice bridging isn't a myth...because we've seen it. Time and time again.
Some suggest waiting until a quarter inch or a half inch of ice has built up, and I disagree with that, too. Ice builds more readily on ice than it does on a rubber boot, and if you let ice build and form over the boot, the rate of accretion , or the rate at which the ice builds, will be greater; more sticks, and it sticks better than it does over the airframe. This is especially true of rime ice, which can build at fantastic rates once it gets started.
Personaly, I advocate letting experience be your guide. If you have soft ice out there and pop or blow the boots too soon, it will bridge, and then it's hard to get off. What is needed is letting just enough ice build that it can be properly broken, and the ability to judge this comes with time. I also advocate staying out of ice where ever possible, and if you do get in ice, get out of it as soon as you can. Very often a simple altitude change will do it, if you make the change soon enough.
I've seen ice build so rapidly that the aircraft loses it's ability to make those changs. I experienced that in a Twin Commander once, in which ice built rapidly enough that 50 knots of airspeed was lost in less than a minute, and altitude could no longer be maintained. We had no choice but to descend, and did until we made contact with a road, and followed the road to a local airfield. It was a very uncomfortable experience, made worse as we were in a mountainous location with severe limitations on our ability to divert, or turn, and once the icing began we could no longer make the minimum enroute altitude. It happened very quickly, and started next to a sharp rise in terrain which pushed a lot of moisture into the freezing level. Our systems couldn't keep up with it.
A case like that calls for immediate agressive activation of all anti-ice and de-ice, and immediate action for diversion, altitude changes, etc. It's very serious.
On that note, you'll study of course the differences between anti-ice (preventing ice) and de-ice (removing ice)...but should understand that it generally works best when applied before entering icing conditions (boots excepted, as they don't do a thing until ice builds, except slightly disrupt the aerodynamic shape of the wing or horizontal stab, or inlet). Hot sufaces must be hot before you enter the ice, and if you're waiting until you're in the ice to turn them on, it may already be too late. This is especially true of stall and pitot anti-ice, inlet anti-ice etc. Turn it on early and keep it on until you're sure you're not in the ice.
Icing occurs above freezing, and continues down to about minus ten to minus 15 celsius. That's the ideal range. Icing can occur above freezing ambient temperatures due both to inaccurate temperature sensors, and from freezing rain and other phenomenae. It can occur due to local drops in temperature around the airframe where airflow is accelerated, pressure drops, and ice forms. (Carburetor icing is a good example). Icing can also occur at very cool temperatures...liquid water, in the form of supercooled water droplets, has been encountered right down to minus 40 degrees. It does happen. In any event, having your heats on and your ice protection active before encountering ice is the best policy...any time you're in icing condtions.
Icing conditions are any conditions that might cause ice, are conducive to ice, are producing ice, in which ice is forecast, in which is is reported, in which ice is possible...even when it's not being reported or forecast. Ice can easily form when it hasn't been forecast. Ice can for when others aren't reporting it...after all, someone has to be the first to experience it...it might just be you.
There's a lot of material out there on ice, and for all the time and experience the industry has with ice, there's a lot more yet to be learned. You certainly live in the right part of the world (Sweden, is it?) for that...learn as much as you can about it, and always assume there's more to learn as you go. Good luck!