I checked it before few minutes and: you'll loose non-transferable Tibia Coins as first .
I had 2030 TC - 1440 red, non-transferable TC and 590 purple, transferable TC.
Then I bought XP Boost for 30 TC. Amount of transferable TC is still the same.
Worth to mention, that non-transferable Tibia Coins in my case are newer, than transferable ones.