sci-calculators/pcalc-1.0.0-r1 had DEPEND="sys-devel/flex sys-devel/bison", whereas sci-calculators/pcalc-1.1 has DEPEND="", but pcalc-1.1 still depends on both.
sys-devel/flex is part of system, see $PORTDIR/profiles/base/packages
You're right. Sorry. The system I encountered this on was installed a long time ago and is little bit messed up...