Why are both log file being written at the same time

Question

I have a strange situation and I would like to get someone else taught.

I have a database that have 2 log files (I know, it should not and I plan of fixing it soon).

Now for what I know, log file are written sequentially (filling up one VLF then the next one) so I would expect the log file with the active VLF to fill up until it "round rubbin" into the next one but this is now what I observed.

Here's the log file usage at my first check:

The fact that both were used at the same percentage is the reason why I checked again a couple of minute later:

Why does both log file fill at the same time ?

I checked and there is no strange trace flag enable on that instance that would explain it.

Thank you for your help.