Sylenth1 in Reaper : run as separate process + embed bridged UI

[dune_rave]

Just observed that I can't use pop up preset selector, or any pop up menu with my mouse
when I run Sylenth1 in Reaper as separate process and the "embed bridged UI" is also turned on.

When only the run as separate process is active, pop ups are working,
so the problem comes when "embed bridged UI" is also turned on.
When this is turned on, the pop up appears, but when I try to move my mouse to select, the pop up disappears. (with left, right, up, down arrows on my keyboard I can select menu items, but I should not move the mouse while doing this)

My environment:
win 10 64bit
Reaper 64bit v5.70
Sylenth1 64 bit v3.03

Dunno if it's Reaper problem or not. I had no problem with other synths (u-he, rob papen, kv331audio).
Anyway, this is not a "serious" thing, I just wrote down my observation.