Just tested it and this is my conclusion: Talent Is not bugged. I tried it with two soldiers with 25 strength. One of them has resourceful talent and one does not. In tactical map soldier with talent can carry 31 and soldier without the talent can carry 25. That is 25% more after rounding.
What is bugged is that on Geoscape it shows encumbrance 34 for the guy with the perk instead of 31.