Not normal, or reported. What are your PC's specs: CPU/GPU/RAM? What format are the files that freeze? How long is the project?
Prior to beginning a project, click OPTIONS | DISK tab and Clear Unused Cache Files. This can also be done during editing to clear unused files.
When loading a project, or files, allow it to fully cache. The green line above all video file thumbnails should complete. 
As changes are made to a clip, there may be some re-caching, but that should take only seconds.
If yours is a complex or lengthy project, or uses high resolution large files, install the 64-bit version.