vst~ is treated as a graphical object : when you crate a subpatch and make it "graph on parent", vst~ is treated as an object having a GUI.

Following is a demonstration of the problem.

tom f

#N canvas 0 0 454 304 10; #N canvas 147 317 524 316 vst_test 0; #X obj 458 285 vst~ 1 1; #X floatatom 14 14 5 0 0 0 - - -; #X msg 73 91 param 0 $1; #X connect 1 0 2 0; #X connect 2 0 0 0; #X coords 0 0 1 1 100 70 1; #X restore 119 29 pd vst_test;