1. Start a TM Merge Translations on a version document with a decent number of textflows (e. zanata-server messages.properties), remember the locale used
2. Click outside the dialog, causing it to go away
3. Start another TM Merge Translations with the same locale
"We were unable perform the operation. Please try again."
It would be better if this particular case gave the error
"A TM Merge is already in progress for this locale."