Set the filter menu's strata to "MEDIUM" to match that of the MainPanel.

diff --git a/Frame.lua b/Frame.lua
index 9880036..521c329 100644
--- a/Frame.lua
+++ b/Frame.lua
@@ -1968,6 +1968,7 @@ MainPanel.menu_toggle_misc:SetPoint("TOPLEFT", MainPanel.menu_toggle_rep, "BOTTO
 MainPanel.filter_menu = CreateFrame("Frame", "ARL_FilterMenu", MainPanel)
 MainPanel.filter_menu:SetWidth(FILTERMENU_DOUBLE_WIDTH)
 MainPanel.filter_menu:SetHeight(FILTERMENU_HEIGHT)
+MainPanel.filter_menu:SetFrameStrata("MEDIUM")
 MainPanel.filter_menu:SetPoint("TOPLEFT", MainPanel, "TOPRIGHT", -6, -102)
 MainPanel.filter_menu:EnableMouse(true)
 MainPanel.filter_menu:EnableKeyboard(true)