I get that often at 1/2 to 3/4 tank coming home in the afternoon if I put the bike right into the garage with temps upper 80s and higher.
I assumed it was the heat from the engine causing the fuel to warm a bit more and venting. Much more noticiable if I left the bike in the sun for a few hours and the fuel in the tank is hot already. I have a small shop fan that I leave on to help cool the bike if I am closing the garage door quickly now. It seems to have helped.
2011 White Vision - Nuvi 550, Lowers, Lloydz 2nd filter, Vic perf filter, CB/Icom, 96 Brake LED's, Clear Signal lens/Switchbacks, VIC Hwy Pegs, Stebel Horn, 7Jurock 15" Shield, PCV, Lloyd ATS and Variable intake, Ness honkers
2004 V92 TC - S1 flash, level 1 slip-on, Ness big sucker K&N, ISO Grips, 4x1.5 Highway Hawg Risers, extra chrome (never too much), JM 2k CB 4' antena, Mustang seat, HD Front TS & Lowers, OD Pulley
Retired Navy SCPO