1) As pointed out by previous contributor, 'ssrvj', this way of worship exist only in Kerala Shiva temples and erstwhile Travancore region, but now in Tamilnadu. (Also adding for information, there are quite few number of Shivatemples in these region, where devotees perform full Pradhakshanam in clock wise direction - Sreekanteswarar temple in Trivandrum and Shiva temples in and around East Fort, Trivandrum and Suchindram, Nagercoil, Tamilnadu).
2) I am not competent enough to explain the reasons for this; however what I have learned is:
"There is believe by devotees not to cross the Abhisheka Theertham flowing from Shiva shrine. So in general they adopt the route - Pray Nandhikeswarar, Shiva; then proceed in anticlockwise direction upto this point of abhisekha theertham flowing, then turn back and perform the rotation in clockwise ending to this point of abhisheka theertham flowing zone."
So this way devotees do complete one full Pradhakshanam.
[Almost all temples of these region have inside and outside prakarams (circular parths around the shrine). As well in the inside prakaram, there likely to have an exit behind Shiva shirne. Hence on completing the pradhakshanam described above, devotees may take the exit behind the Shiva shrine and perform the full pradhakshanam in clockwise in the outer prakaram].