Hotbar not acting normally

Items in my hotbar are not switching properly. Its happened twice so far, in the last time I was useing torches and then switched to a block and the hot bar showed i selctected a new block but still placed torches no block i selected would change this. I had to log out to fix it. I thought it could be lag but i have high speed internet and didnt experience any lag anywhere.  First time was same thing but with signs.