We realized some time ago that the BIG-IP GUI does not handle UTF-8 encoded strings very well in Data Groups which result in ever growing data records for everytime the Data Group is saved.
This is an example on how to reproduce the problem and to see it in action:
Start by creating an empty new data group named TEST of the type string.
Add a line with the key test1 and the value abcåäö123 (copy and paste if you don't have a nordic keyboard)
Check with tmsh list ltm data-group internal TEST
Youwillsee that it doesn't handle the UTF-8 data and you will se two characters for each > 7-bit character.
Now go to the GUI again and add a second line with the key test2 and the same value abcåäö123
Onceagainchecktmsh and youwillsee that not only has test2 been added but test1hasalsobeenupdated, now including even more wrong characters.
This is a screenshot of how it will look:
The result of this is that eventually you will receive the following error from the BIG-IP (even if you only update lines that are not containing 8-bit ascii characters).