In Poser 5 SR4 this is a known "bug" (actually it's claimed to be a feature) You need to open the LibraryPrefs.xml (in the Poser 5Runtimeprefs folder) and change the PreviewNum=100 to something larger. I set mine to 500. You can make a copy of the file first, just in case.

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You just can't put the words "Poserites" and "happy" in the same sentence - didn't you know that? LaurieA
  Using Poser since 2002. Currently at Version 11.1 - Win 10.