I don't see that on my system.

I did replace the second shell command with xterm -e htop and it did pop up a new xterm running htop while still filling in the first text widget, exactly as expected.

You can watch it here (YouTube warning!)

Interestingly, when I click into the area to be filled, the application responds, but it immediately gets stuck again.

map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]

Best guess so far: you are dumping (hundreds of)? thousands of lines into the text widget. This is what is taking time.

Sort of confirmed, instead of just 'find' try

q( find / 2>/dev/null | perl -pe '$| = 1; select undef, undef, undef, 
+0.01' )
[download]

This feeds in the lines just a little slower :)