The progress bar on Workbench is apparently no good indication. I have grown into the habit of waiting an additional minute before removing the thumbdrive and had no data loss since.
why that i wonder. i would likely report the issue, if such was ever the case on my system. on my a4k/deneb ive never been able to get fat95 filesys corrupt even by accidentaly removing the media while writing. in fact there was a hangup issue way back, while in dma mode copying large files (like 100's of mb), but it must have been taken care of after ive reported it. was probably due to newly discovered buster bug. also i must yet buy a stick that doesnt get recognized under poseidon.
