Yes they are because they work for me if I use them alone.
More over I know for a fact that the same situation with a different status effect in 1.8.7 works and properly overrides it.
/effect @p levitation 9999 10 true
/effect @p levitation 9999 250 true
Tested on singleplayer.
Sorry, I didn't word myself properly. Edited now. I do know it's /effect <selector> <id> <time> <lvl>
What you suggested works, but it doesn't fix the issue. This worked for levels as big as 250 in 1.8.7 so it is a bug.