Memory issue with UIGETDIR

Recently, I have noticed an odd behavior from uigetdir function of MATLAB.

If I have a string with some values, it has almost no effect on the memory.

    >> memory
    Maximum possible array:    860 MB (9.014e+08 bytes)
    Memory available for all arrays:   1287 MB (1.349e+09 bytes)
    Memory used by MATLAB:    435 MB (4.557e+08 bytes)
    Physical Memory (RAM):   3317 MB (3.478e+09 bytes)

    >> folder = 'C:\Users\MrAwesome';

    >> memory
    Maximum possible array:    860 MB (9.014e+08 bytes) *
    Memory available for all arrays:   1289 MB (1.352e+09 bytes) **
    Memory used by MATLAB:    434 MB (4.553e+08 bytes)
    Physical Memory (RAM):   3317 MB (3.478e+09 bytes)

But if I use uigetdir instead, it drains down a whole lot of memory:

    >> folder2 = uigetdir;

    >> memory
    Maximum possible array:    727 MB (7.628e+08 bytes) *
    Memory available for all arrays:   1153 MB (1.208e+09 bytes) **
    Memory used by MATLAB:    458 MB (4.806e+08 bytes)
    Physical Memory (RAM):   3317 MB (3.478e+09 bytes)

And if I clear these two variables from my memory, it will not release the memory!

I looked it up, and found nothing on this issue anywhere.

First, I would like to know how to use (or what to use instead of) uigetdir effectively?

Second, I would like to know how to free the memory from some functions/variables like this?