@ddepre 

Is there a red button on the top right corner that is "Save"? If so, you need to save it. Apply is not equal to Save. 

Why would you change the default VLAN? In my best memory, I don't remember that the default VLAN is changeable. You cannot modify the Name or VLAN ID. On the high-end switches, the default VLAN edit button is even "grey out"

  @John1234 

The base problem is that I want to change which VLAN1 ports will be tagged or untagged.
When trying to apply this change - the remark "Default_VLAN" a message "VLAN Name should not be more than 10 Characters..." appears.

Changing the name is not accepted - nor by the apply nor by the save button .

As a result  the changes for tagged/untagged ports are also not accepted.

The VLAN1 name is of no importance (to me).

In TL-SG108E V2 and V6 switches this is possible.

  @ddepre 

Can I know what the point of tagging VLAN 1 is? There is no need to tag the default VLAN from my paste exp.

  @John1234 

Trying to build a setup similar to the 2nd example in :

https://www.tp-link.com/us/support/faq/788/

  @ddepre 

Sorry that your picture is very small. Are you modifying the VLAN 1? If you are modifying VLAN1 and it tells you it cannot be saved due to the name, it's like a bug. 

  @ddepre I have the same issue.

Historically the switches worked fine for many years. I've went to change some VLAN assignments for a port and noted VLAN1 has appeared untagged across ports 1-8, despite also having my VLAN30 untagged. 

I'm fairly sure in the past I had VLAN1 in existence but no ports were selected for tagging or untagging. I also don't recall this issue myself, however it's rare I need to reconfigure ports on my home network. Regardless, I'm unable to remove VLAN1 being untagged on any port despite having already an untagged VLAN on that port. Process:
Go into 802.1Q VLAN tab

Select VLAN1. The VLAN Name shows "Default_VLAN" 

Change port assignment

Apply

Message displayed saying VLAN name can't be more than 10 characters

Click into VLAN Name. Note, the "Default_VLAN" name disapears as soon as the mouse is over the field

Enter a name <10 characters, hit apply. This is met with "operation succeeded". Hit save. "Save successful"

Go to any other page and return to the 802.1Q VLAN tab and the changes are all reverted as if nothing had happened / been saved. 

Likewise, tagging VLAN1 isn't possible on any port. The same issues occur. 

Basically both my custom VLAN30 AND VLAN1 must be untagged. On any ports which are tagged, they must also be untagged in VLAN1.

I don't think this is a major problem however (otherwise I'd have noticed DHCP being answered by ports in VLANs other than the one I intended i.e. VLAN20 and VLAN40) as the PVID setting is controlling the true port which is untagged. Meaning, despite having VLAN1 and VLAN30 untagged, as the PVID against the port is set to 30, another port which is untagged VLAN20 (and therefore VLAN1 too) using the PVID value 20 won't receive traffic.

I understand this may behaviour (although very badly managed in the UI) may be to prevent lockouts to the admin interface but it's very frustrating for someone who knows how to VLAN and is a huge contrast to say a HP switch which allows VLAN1 to be excluded completely on all ports if the admin configures it in this way.