Photoperiods behaving like autos

Have noticed my last few grows that occasionally I'll get a pheno(photoperiod) that grows just like a auto. Start my seeds outdoors so no light switch from artificial could be responsible for it. Have seen it with more than one strain also. When the other plants are starting to flower, this pheno will be finishing up. Has anyone else experienced this?

i see it happen when i let the photos get rootbound. Never really phased me, i know it was my fault when i see it cuz i left them in the undersized pot too long.