A scrollbar that is initially drawn correctly disabled, gets enabled as soon as you click the triangle

0.4.11-RC-23-gb5fef42 gcc dbg linux

The installer of "SciLab 5.5.2" from rapps properly displays its horizontal scrollbar disabled currently. Fine.

But as soon as you click on the triangle (which is correctly drawn disabled as well), the scrollbar gets drawn enabled erroneously.
The disabled triangle should never have any effect upon clicking on it.
0.4.11-RC-23-gb5fef42__scrollbar.webm
0.4.11-RC-23-gb5fef42__scrollbar.log (nothing is logged upon that click)