When I run pd it just hangs here:

$ pd
priority 6 scheduling enabled.
priority 8 scheduling enabled.

I suspect it's only a gui issue, and probably the backend runs, because if I run pd-gui.tcl I get:

$ pd-gui.tcl
Error in startup script: can't find package pd_connect
while executing
"package require pd_connect"
(file "/usr/bin/pd-gui.tcl" line 26)

however pd_connect.tcl was installed:

$ pacman -Ql pd |grep pd_connect
pd /usr/lib/pd/tcl/pd_connect.tcl

Now,

$ which pd-gui.tcl
/usr/bin/pd-gui.tcl

but there's another file named like that installed by the package:

$ pacman -Ql pd |grep pd-gui.tcl
pd /usr/bin/pd-gui.tcl
pd /usr/lib/pd/tcl/pd-gui.tcl

and if I run /usr/lib/pd/tcl/pd-gui.tcl, the gui does indeed start but many parts of it are black, and I can't see patches (see attached screenshot).

I immagine this has something to do with pd looking for files in wrong places, but this is as far as I could get in tracking down the cause.