QFileDialog slows down with multiple selection on GTK 3.0

When running a gtk 3.0 system, when coming back from a multiple file selection, the application waits a long time before becoming available again. This time is variable but increases with the number of files selected. Note that the time is really small if only one or two files are selected, but can reach 8 seconds for about 60 files, 12 seconds for 90 files.

I attach an extremely simple that reproduces the problem. You will see in the example that the getOpenFilenames function comes back instantly and the code following it is executed right away. It's only when coming back to the main event loop that it stalls for a long time.