Trello – Troubleshooting Actions Failing Inside Work Firewall

When I use Trello at work, certain specific actions consistently fail to get persisted back to the server. The two that I am always having issues with are:

• Removing labels
• Deleting items from checklists

As an example, let's say I create a new card and assign label A. I then come back later and remove label A, but assign label B.

The outcome is at first an orange message in the top right corner:

Sending…

This is followed by a red message in the top right corner:

Connection interrupted. Retrying 1 action.

This message never goes away. If I refresh Trello, the card will have both labels A and B assigned.

My workaround at the moment is to open the Android app on my phone and remove the label.

I'm guessing this is related specifically to our work environment – the firewall, proxy, ISA server, etc. I have tried using Fiddler to see which specific HTTP requests are failing, but as soon as Fiddler is hooked in as a proxy all external web sites stop working.

My question is, does anyone know what is special about these specific actions and why they might be failing inside my work firewall?

Note – I don't believe this a bug in Trello as it works perfectly outside of work!