Problem:

Why when I open my log files in CMTrace is it incomplete/ truncated?

Resolution:

You will only see this issue if you are viewing a log in the Configuration Manager CMTrace log viewer that has more than 8,000 lines (line 8,001+ aren’t shown).

This is a known issue as documented in Microsoft KB Article 2716956
Using the System Center 2012 Configuration Manager CMTrace log viewer to review a log that contains a line exceeding 8000 characters causes the log to be truncated

UPDATE: SP1 of ConfigMgr 2012 includes an updated version of CMTrace that resolves this issue.