I think that the answer to this question should be a little more detailed.
All fixes and improvements are making only for the trunk:
https://svn.freepascal.org/svn/lazarus/trunk/After this most fixes will merged in fixes branch, but not all.
The reasons may be different. For example, may be big difference between some part of code in trunk and in fixes branch. So, some fixes will appear only in next major version (1.10 or 2.0) but not in minor (1.8.2, 1.8.4)
Fixes that will be merged (or already merged) you can see here:
http://wiki.lazarus.freepascal.org/Lazarus_1.8_fixes_branch