ContentFeatureSource.getCount(query) does not return correct sizes if all of the following conditions are met:
1. The implementing class has canOffset() = false
2. The implementing class has canFilter() = false
3. The implementing class supports getCountInternal() as long as the filter is Filter.INCLUDE
4. The query has a startIndex greater than zero
5. The query has a filter of Filter.INCLUDE
Under these conditions, ContentFeatureSource.Count() will ignore the effect of startIndex on the feature count.
This affects PropertyFeatureSource (from the gt-property-ng module) and (most likely) CsvFeatureSource.
Observed on the latest master build.