There appears to be an issue with scrollCollapse enabled that causes the number of rows to be loaded initially to be less than expected.
This appears to be a similar issue to the one described here: https://datatables.net/forums/discussion/31165/problem-with-initial-display-when-using-scroller-with-serverside-scrollcollapse
The following is a test case that reproduces the issue using the nightly builds: http://live.datatables.net/qopijexe/1
This appears to happen in both Firefox and IE11. For Chrome, this issue only occurs if the viewport is sufficiently small. About half the width of the table should work.
This has been tested on Chrome, Firefox, and IE11 in both CentOS 7 and Windows 7.