QPlainTextEdit memory leak

I wrote a simple app with Qt 5.9.6, I ran that and wondered the used memory is growing. After tracing/debugging my application, I realized something about QPlainTextEdit !!!

The memory leak was for a qplaintextedit as a scratchpad in my app, but after every use of that, I used the clear() function to blank it for next use.

But the used memory by that scratchpad woudn't be released!

I decided to test it

I opened a new project, containing a QPlainTextEdit & a QPushButton(to call clear() function).

• After run, the used memory was 9.7MiB
• Entered some long text to QPlainTextEdit, the used memory was 52MiB
• Pressed the QPushButton(clear() the QPlainTextEdit), the expected used memory is 9.7MiB, but it was 52MiB.

I tried delete, static allocation, dynamic allocation..., many ways to manage that, but no different!

What's wrong with QPlainTextEdit ?