Weak key schedule IDEA Why was such a weak key schedule chosen for IDEA?

The key schedule of IDEA works like this:
Divide the key (128 bit) into 8 round keys, each 16 bit long. This are the first 8 "round" keys (6 keys per round). Rotate the original key by 25 bit to the left. Repeat this until we got the needed 52 round keys for 8.5 rounds. (4 keys for the last "half" round.)
This key schedule is fully linear and patterns in the key exist even in the last round keys with nearly no change. A high number of zero bits in the key is very problematic for the cipher because the number stays the same through the whole key schedule. Many attacks exploit this behavior.

This can be seen with a small example encryption. (Key ($K$) and plaintext ($P$) in hexadecimal formatting, leading zero bytes were omitted. )
  $$ K = 00, P = 00, \operatorname{IDEA}(K,P) = \text{0001 0001 0000 0000} $$
  $$ K = 00, P = 01, \operatorname{IDEA}(K,P) = \text{0013 fff5 0012 0009} $$
  $$ K = 00, P = 02, \operatorname{IDEA}(K,P) = \text{0191 0059 011c ff32} $$
  $$ K = 00, P = 03, \operatorname{IDEA}(K,P) = \text{038f 0099 02d6 fe33} $$
  $$ K = 00, P = \text{01f0}, \operatorname{IDEA}(K,P) = \text{1841 fbc1 ef20 f270} $$
  $$ K = \text{0d50}, P = 00, \operatorname{IDEA}(K,P) = \text{3fb2 5ff2 055d 16a6} $$
(Source: IDEA calculator (Java))

Further analysis of the data and the encryption process shows very slow avalanche effect when high amount of zero bits were in the plaintext or ciphertext. Why was this not recognized and solved? Was this kind of problem not known at the time as IDEA was invented? Or is this no real problem because of the low probability of this effect on random keys?

The paper "Weak Keys for IDEA" (1993, PDF) shows that even a small correction could solves this problem, like the XOR of a constant to every round key before using it. The constant $\text{0dae}$ (16 bit, hexadecimal notation) was chosen as an example, but the exact value is not critical to solve the problem as stated by the paper. 

Are there any papers which descripe the development process of IDEA? Maybe they could explain some thoughs about the key schedule.
Such a weak key schedule was chosen since the key schedule "theory" was not well developed by that time. Designers just modified the key schedule of DES a bit. Remember that these key schedules had to be optimized for hardware, and any extra operation would cost something in terms of area.