Created attachment 233293 [details]
Use Linux with (for example) Latin Modern Math fonts installed.
Go to the MathML torture test and check test 22 with "Latin Modern Math" item selected. If you zoom in and then out, the size of the horizontal braces is not updated.
If wonder if the problem is due to the fact that the stretchSize() is included in the preferred width computation and the m_stretchWidth is cached on the renderer object. Perhaps the stretch width should instead only be taken in consideration in RenderMathMLSpace::updateLogicalWidth(), like what is done for mspace.
This issue is fixed on Alex's MathMLLayout branch.
Not sure which patch fixes the problem, but let's make it depend on bug 155018
Fixed by r202420.