Before 0.6, FCPX only "played" drop zone media for the length of the effect as it was created. A 5 second effect would only play drop zone media for 5 seconds. If you stretched out the effect (title, generator) longer, several things could happen:
1) the effect had no "special" markers
FCPX would time stretch the drop zone media. For the 5 second effect mentioned above
FCPX would only use 5 seconds of the clip no matter how long you stretched out the effect. If you stretch out the effect to 10 seconds, the media plays at 50% speed. Shrinking to 2.5 seconds increased the speed to 200%.
2) the effect had a "build in" marker
FCPX would play the media for the correct timing up to the end of the build in marker THEN it would time stretch, up to a build out marker, if one was present, or the end of the effect/template.
3) the effect had a build out marker (only)
FCPX would not play the media until the original length of the effect and its drop zone was left, then it would play the media as an "outro". If any time was set *before* the build out marker -- it would be time stretched from the beginning up to the build out marker.
4) the effect had a project loop marker
FCPX would play the original length of the effect/drop zone at the correct speed, over and over until the effect "ran out". If a build in marker was also used, the media would loop between the end of the build in and the project end loop marker. Anything created past a loop marker was ignored.
A lot of effects were built with these rules in mind (and so were many of mine). To get around the limitations, it was necessary to "cut" the drop zone media to exactly match the length of the effect template. Bringing a clip into the storyline (usually as a connected clip) made it easy to cut the clip into starting and ending frames, then duplicating the effect repeatedly until the actual playing length you needed was exhausted.
10.0.6 has change this behavior somewhat. I haven't tested out all the variants above (but based on your question, I'd say the marker behaviors are the same), but a "regular" drop zone in an effect (no markers at all) will now play dropped media at normal speed even if you stretch out the effect -- until the clip ends (or the effect does), then FCPX will simply freeze frame the rest of the length. If you have Motion, you could try going in and deleting the markers (and Save As a different copy in case something goes wrong and the effect doesn't work right afterwards -- there could be other reasons for the markers being present.)