Board Thread:Bug Reports/@comment-137.118.200.204-20170420012547/@comment-26347028-20170420193342

Direranger50 wrote: Try looking in your controls. There is a pick block button, and if you have sand on you it will bocome selected if you look at it and push that button. I would've deemed it unlikely to be a problem reported from the creative mode, but it's certainly a possibility.

Much more likely to be a different mod, though.