Mobility boot's giving the wrong stats

Dear Riot I just played a custom to confirm this bug with mobility boot's stats. I go from getting +20 (6% from runes [4.5%] and masteries [1.5%]) then after buying mobility boots with alacrity upgrade (which is +105 [out of combat] +20 [Alacrity] total +125) i get a total of 138. now simple math is 20+125=145 can you please tell me where the missing 7 is going please.