Tested with r12684 on Mint18 (wx3.0.2 with GTK2.24.30).
To reproduce:
Expected result: the main window opens, then the floating toolbar opens on top.
Observed result: the floating toolbar appears first, then the main window opens on top hiding it.
On MSW there is no problem (after [r12684], see ticket [#1156] for more information).
Diff: