Showing custom tab in tray (instead of current) breaks Paste and Copy Next

**Description of possible bug**
Choosing a custom tab in tray, instead of `current` (the default) breaks Paste and Copy Next

**STR**
1. Go to preferences / Tray
2. Untick `show current tab in menu` (eg in the tray menu)
3. Leave the default option in the drop-down, which I think is `&clipboard`
4. Save (ok) and leave the CopyQ window
5. In a text field, do "Paste and Copy Next"
6. do it a second time

**Expected behavior**
Pastes first item, copies next item, pastes the second item

**observed behabiour**
Pastes last item, doesn't copy next, paste the same item again and again.

I had changed this option many days ago, for unrelated reasons, so it took me some time to find the connection. But as soon as I went back to default, Paste and Copy Next started working again.
I tried to find open and closed issues about this, so I tried to wait longer before first and second "Paste and copy next", to emulate a longer "sleep" function, didn't work.

**Version, OS and Environment**
```
CopyQ Clipboard Manager 6.2.0~bionic
Qt: 5.9.5
KNotifications: 5.44.0
Compiler: GCC
Arch: x86_64-little_endian-lp64
OS: Linux Mint 19.1
```
Cinnamon 4.0.10