When direct rollover happens from 401K to Traditional IRA. Will the entry be under 4a/4b IRA or will it be under 5a/5b Pension and Annuities.

This is a distribution from the 401(k) so it goes on lines 5a/5b Pensions and annuities.  A 401(k) is not an IRA.

What if it is the opposite situation, and it is a trustee-to-trustee direct rollover from a traditional IRA to a 401k? Should the entry be under 4a/4b IRA or 5a/5b Pension and annuities? 

I have a direct rollover IRA to 401k, and it is showing up under the 5a/5b section is that correct?

No, it should be on 4a for a nontaxable IRA distribution. If the distribution is from an IRA, it should appear on 4a. If it does not, verify whether the IRA box is checked on Form 1099-R. 

@LJ315