Unit deserting upon capturing enemy province

Hey, is this just something that normally happens or a bug?

I have just send a brigade of armored cars to capture an unprtected enemy province and did so succesfullly.

I got the notification that i conquered it and all. But when i looked at it again, my brigade was gone and there was only a brigade of armored cars of my enemy, that wasn't there before and has the same condition as my brigade. I thought it might be a visiual bug, so I reloaded the page, only to see that now the province was in enemy hands again, without me getting a notification that I lost the province to the enemy.

tl:dr I send a unit to capture an undefended province, upon capture my unit disappears and an enemy unit with the exact same condition takes it's place and recaptures the province without a notification

I am royally confused