Ideally, if it is a useful fix or feature, send it to us & we will encorporate it into a future release. This helps to improve the library.
My earlier post was probably not actually correct re redistribution of source. I just read the license now and here is a bit of a summary (IANAL).
If you modify the library and wish to distribute the modified library, the LGPL applies to this derived work. In addition, you can't charge for the derived work, and the modified source must be distributed with the derived work (as must the licence).
If you are not redistributing the derived work, you don't need to distribute the source. However if you have made improvements that would be useful to others, we'll appreciate your sending them to us.
Note, however, that if you copy code from the library into your application, you agree under the terms of the license that your application is under the LGPL. To avoid this, use it solely as a library - don't cut and paste it into your code.
For more info see
All right, let's say I'm modifying the code.
What should I do? Just give the modifyed code whoever will ask?