Sorry for my English is unskilled.
I received the help of a machine translator.

Problem
When you input some seed string to create a new world, the input process will ignores some of the 'normal' values entered by the user, or the input process will ignores all of the user input and determining a seed value randomly.

Some cases makes unwanted seed values(especially "My seed was suddenly changed to zero!"), or it causes different world by same seed input.

Details
If you input a seed string that starts with numbers, the input process receives only numbers.
For examples,

• 0xdeadbeef
• 01234
• 0000
• 0_
• 0oTESTo0
• 0(white spaces)
  ... All of these are the same world by seed 0. Because it is truncated to '0'.

Another examples,

• 1234 -> Seed value has 1234. No problem.
• 1234abc -> Seed value has 1234. This world is the same as the above.
• 1234abc1234abc -> Seed value has 1234. Same as above.

• abc1234 -> Seed value has result of hashcode for the string "abc1234". No problem.
• abc1234abc -> Seed value has result of hashcode for the string "abc1234abc". No problem. This world is not the same as the above.

• 1234567890abc -> Seed value has 1234567890.
• 12345678901abc -> Seed value has result of hashcode for the string "12345678901". In other words, it is the same world as seed string "12345678901".

If you input a seed string one character, the input process will ignores all of the user input and determining a seed value randomly. (like empty seed.)
For examples,

• 0 -> Seed value has result of random.
• 1 -> Same as above.
• 2 -> Same...
• a -> Same...
• z -> Same...
• 11 -> Seed value has 11.

It doesn't help some user who wants a new world by one character seed.

I don't know if this process is intended. So I reported this as a bug. Thanks.

Test Environment
Pocket Edition 0.14 on Vega Iron A870S.
Windows 10 Edition 0.14.1

Edited : Fixed some ambiguous sentences and added some more examples.