I have written this, but nothing's happened. After releasing left mouse button, Gliph still restores original position.
What the stupid?
Did you rebuild LCL?
You've modified the LCL unit. To see changes in action you need to rebuild LCL and then rebuild the application.
Select from menu Tools -> Configure "Build Lazarus" -> Quick Build Options. select "Build LCL" at "Build options" and then press "Build" bottom.
I even tried to rebuild Lazarus, but unsuccessfully. So toolbutton.inc file unrelated to Lazarus. What purpose is toolbutton.inc for?
Why was it unsuccessfully? It feels like you've rebuilt Lazarus IDE only, without rebuilding LCL first.
As for the purpose of toolbutton.inc, I'm sure you can find the answer just by looking at ComCtrls unit.
Where is r26740? I can see r26728 only!
I guess you're looking at Daily Snapshots.
26740 is already available where:
http://www.hu.freepascal.org/lazarus/Though not for win64, of some reason.