Its not bugged, read the skill description better next time.
From iRO Website:
Quote:Sprint
Enable the caster to run with incredible speed. At levels 7 and above, this skill endows the caster with the Spurt status, which will temporarily increase STR for 150 Seconds if the caster stops running and is barehanded. Spurt status is canceled if the caster equips a weapon. Each level of the Sprint skill increases its user's barehanded damage by +10.
Quote: Tumbling
Enable a 20% chance of blocking long ranged physical attacks. When caster is in Spurt status (after performing Lv 7 Sprint or higher), Tumbling will also block other kinds of attacks.
other kinds of attacks = melee.
