sometimes if you place a slab against another slab which is upsidedown (so that you can place redstone and torches on them) it doesn't get placed upside down

the following video is part of a video BdoubleO100 uploaded on yt:
https://youtube.googleapis.com/v/CC6bBaoUPt8?start=1160&end=1192
it pretty much shows the issue (even 3 times in a row!)

maybe it has something to do with the server (lag or server load as a potential issue?)

I'm sorry if the issue has been posted here already but the search didn't give me any results (no full text search for the data base with bug reports and no div with similar results containing reports with only some of the words you searched for) -> you can barely search for complex issues if you don't know how others would explain them... (English is not my native language)