Duplicate commands triggered from single Clipboard copy

I really struggled writing a command to send a copied link from Chromium to Firefox, because the links were almost always opened twice.

**To Reproduce**

* Create an "Automatic" command
* Matching Content "^http"
* Command: `copyq: open(str(data('text/plain'))`

**Expected behavior**
One browser tab is opened when some http url is copied.
Instead I get 2 browser tabs!

**Version, OS and Environment**
- Application Version v3.8.0
- OS Linux Mint 19
- Desktop environment: Cinnamon

**Additional context**
The following "Command" script avoids and illustrates the issue:
```
copyq:
var incoming = str(data('text/plain'));
var prev = str(read(0));
if (incoming == prev)
popup("REPEATED!", incoming+'\n==\n'+prev);
else
open(incoming);
```