Bug on off-canvas with other modules

I am testing some modules that are not compatible with offcanvas t3 bs3.
For example japanel Link:

It works all right until the offcanvas button is pressed.
Once pressed, you have to refresh the page to return to the module function correctly.

I found the solution by adding the following line to custom.css:

.t3-wrapper {position: initial;}

Is this correct?
Why t3-wrapper takes a position in relative?