ebuild was edited. From changelog of ebuild: 22 Feb 2011; Ulrich Mueller <ulm@gentoo.org> gnuplot-4.2.6-r1.ebuild, gnuplot-4.4.2.ebuild: Don't link against media-libs/pdflib, because it would violate clause 2.1 of the PDFLite license. Configure --without-pdf, bug 356005. Drop unnecessary x11-libs/gtk+ dependency with USE=cairo. But same versions are kept on ebuild after being edited. Gnuplot ebuild should have -r1 or something to indicate a rebuild since media-libs/pdflib is now masked. Misstake to change the ebuild without updating versions.
Hm, I had assumed that removal of the pdf USE flag would trigger a rebuild with emerge --newuse. Seems that this assumption was not valid. Bumped to 4.2.6-r2 and 4.4.2-r1.
(In reply to comment #1) > Hm, I had assumed that removal of the pdf USE flag would trigger a rebuild with > emerge --newuse. Seems that this assumption was not valid. Only if you use this feature.