It's just an issue of memory not being freed. There's no such thing as a memory purge. When a object is resized it's physics shape is re-created, so presumably the old shape isn't being freed. To fix it the plugin needs to be corrected, or worst case it's an issue with the physics library itself that would need to be corrected.
As a user to get it fixed you have a few options:
1. Report it to the bugs forum following the reporting guidelines. Likely there is some kind of triage of what gets fixed, but this alerts the creator, who is most familiar with the code, about the problem.
2. Dive into the plugin code and find a fix yourself. Not easy, but a good learning experience although likely time consuming. If a fix is found then alerting the developer in the bug report is a good way to have the plugin officially fixed if it's a good solution.
3. Use another physics plugin. You could try the chipmunk physics plugin. It doesn't have the memory issue.